duktape-1.5.2/src-separate/duk_regexp_executor.c

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/*
 *  Regexp executor.
 *
 *  Safety: the Ecmascript executor should prevent user from reading and
 *  replacing regexp bytecode.  Even so, the executor must validate all
 *  memory accesses etc.  When an invalid access is detected (e.g. a 'save'
 *  opcode to invalid, unallocated index) it should fail with an internal
 *  error but not cause a segmentation fault.
 *
 *  Notes:
 *
 *    - Backtrack counts are limited to unsigned 32 bits but should
 *      technically be duk_size_t for strings longer than 4G chars.
 *      This also requires a regexp bytecode change.
 */
 
#include "duk_internal.h"
 
#ifdef DUK_USE_REGEXP_SUPPORT
 
/*
 *  Helpers for UTF-8 handling
 *
 *  For bytecode readers the duk_uint32_t and duk_int32_t types are correct
 *  because they're used for more than just codepoints.
 */
 
DUK_LOCAL duk_uint32_t duk__bc_get_u32(duk_re_matcher_ctx *re_ctx, const duk_uint8_t **pc) {
    return (duk_uint32_t) duk_unicode_decode_xutf8_checked(re_ctx->thr, pc, re_ctx->bytecode, re_ctx->bytecode_end);
}
 
DUK_LOCAL duk_int32_t duk__bc_get_i32(duk_re_matcher_ctx *re_ctx, const duk_uint8_t **pc) {
    duk_uint32_t t;
 
    /* signed integer encoding needed to work with UTF-8 */
    t = (duk_uint32_t) duk_unicode_decode_xutf8_checked(re_ctx->thr, pc, re_ctx->bytecode, re_ctx->bytecode_end);
    if (t & 1) {
        return -((duk_int32_t) (t >> 1));
    } else {
        return (duk_int32_t) (t >> 1);
    }
}
 
DUK_LOCAL const duk_uint8_t *duk__utf8_backtrack(duk_hthread *thr, const duk_uint8_t **ptr, const duk_uint8_t *ptr_start, const duk_uint8_t *ptr_end, duk_uint_fast32_t count) {
    const duk_uint8_t *p;
 
    /* Note: allow backtracking from p == ptr_end */
    p = *ptr;
    if (p < ptr_start || p > ptr_end) {
        goto fail;
    }
 
    while (count > 0) {
        for (;;) {
            p--;
            if (p < ptr_start) {
                goto fail;
            }
            if ((*p & 0xc0) != 0x80) {
                /* utf-8 continuation bytes have the form 10xx xxxx */
                break;
            }
        }
        count--;
    }
    *ptr = p;
    return p;
 
 fail:
    DUK_ERROR_INTERNAL_DEFMSG(thr);
    return NULL;  /* never here */
}
 
DUK_LOCAL const duk_uint8_t *duk__utf8_advance(duk_hthread *thr, const duk_uint8_t **ptr, const duk_uint8_t *ptr_start, const duk_uint8_t *ptr_end, duk_uint_fast32_t count) {
    const duk_uint8_t *p;
 
    p = *ptr;
    if (p < ptr_start || p >= ptr_end) {
        goto fail;
    }
 
    while (count > 0) {
        for (;;) {
            p++;
 
            /* Note: if encoding ends by hitting end of input, we don't check that
             * the encoding is valid, we just assume it is.
             */
            if (p >= ptr_end || ((*p & 0xc0) != 0x80)) {
                /* utf-8 continuation bytes have the form 10xx xxxx */
                break;
            }
        }
        count--;
    }
 
    *ptr = p;
    return p;
 
 fail:
    DUK_ERROR_INTERNAL_DEFMSG(thr);
    return NULL;  /* never here */
}
 
/*
 *  Helpers for dealing with the input string
 */
 
/* Get a (possibly canonicalized) input character from current sp.  The input
 * itself is never modified, and captures always record non-canonicalized
 * characters even in case-insensitive matching.
 */
DUK_LOCAL duk_codepoint_t duk__inp_get_cp(duk_re_matcher_ctx *re_ctx, const duk_uint8_t **sp) {
    duk_codepoint_t res = (duk_codepoint_t) duk_unicode_decode_xutf8_checked(re_ctx->thr, sp, re_ctx->input, re_ctx->input_end);
    if (re_ctx->re_flags & DUK_RE_FLAG_IGNORE_CASE) {
        res = duk_unicode_re_canonicalize_char(re_ctx->thr, res);
    }
    return res;
}
 
DUK_LOCAL const duk_uint8_t *duk__inp_backtrack(duk_re_matcher_ctx *re_ctx, const duk_uint8_t **sp, duk_uint_fast32_t count) {
    return duk__utf8_backtrack(re_ctx->thr, sp, re_ctx->input, re_ctx->input_end, count);
}
 
/* Backtrack utf-8 input and return a (possibly canonicalized) input character. */
DUK_LOCAL duk_codepoint_t duk__inp_get_prev_cp(duk_re_matcher_ctx *re_ctx, const duk_uint8_t *sp) {
    /* note: caller 'sp' is intentionally not updated here */
    (void) duk__inp_backtrack(re_ctx, &sp, (duk_uint_fast32_t) 1);
    return duk__inp_get_cp(re_ctx, &sp);
}
 
/*
 *  Regexp recursive matching function.
 *
 *  Returns 'sp' on successful match (points to character after last matched one),
 *  NULL otherwise.
 *
 *  The C recursion depth limit check is only performed in this function, this
 *  suffices because the function is present in all true recursion required by
 *  regexp execution.
 */
 
DUK_LOCAL const duk_uint8_t *duk__match_regexp(duk_re_matcher_ctx *re_ctx, const duk_uint8_t *pc, const duk_uint8_t *sp) {
    if (re_ctx->recursion_depth >= re_ctx->recursion_limit) {
        DUK_ERROR_RANGE(re_ctx->thr, DUK_STR_REGEXP_EXECUTOR_RECURSION_LIMIT);
    }
    re_ctx->recursion_depth++;
 
    for (;;) {
        duk_small_int_t op;
 
        if (re_ctx->steps_count >= re_ctx->steps_limit) {
            DUK_ERROR_RANGE(re_ctx->thr, DUK_STR_REGEXP_EXECUTOR_STEP_LIMIT);
        }
        re_ctx->steps_count++;
 
        op = (duk_small_int_t) duk__bc_get_u32(re_ctx, &pc);
 
        DUK_DDD(DUK_DDDPRINT("match: rec=%ld, steps=%ld, pc (after op)=%ld, sp=%ld, op=%ld",
                             (long) re_ctx->recursion_depth,
                             (long) re_ctx->steps_count,
                             (long) (pc - re_ctx->bytecode),
                             (long) (sp - re_ctx->input),
                             (long) op));
 
        switch (op) {
        case DUK_REOP_MATCH: {
            goto match;
        }
        case DUK_REOP_CHAR: {
            /*
             *  Byte-based matching would be possible for case-sensitive
             *  matching but not for case-insensitive matching.  So, we
             *  match by decoding the input and bytecode character normally.
             *
             *  Bytecode characters are assumed to be already canonicalized.
             *  Input characters are canonicalized automatically by
             *  duk__inp_get_cp() if necessary.
             *
             *  There is no opcode for matching multiple characters.  The
             *  regexp compiler has trouble joining strings efficiently
             *  during compilation.  See doc/regexp.rst for more discussion.
             */
            duk_codepoint_t c1, c2;
 
            c1 = (duk_codepoint_t) duk__bc_get_u32(re_ctx, &pc);
            DUK_ASSERT(!(re_ctx->re_flags & DUK_RE_FLAG_IGNORE_CASE) ||
                       c1 == duk_unicode_re_canonicalize_char(re_ctx->thr, c1));  /* canonicalized by compiler */
            if (sp >= re_ctx->input_end) {
                goto fail;
            }
            c2 = duk__inp_get_cp(re_ctx, &sp);
            DUK_DDD(DUK_DDDPRINT("char match, c1=%ld, c2=%ld", (long) c1, (long) c2));
            if (c1 != c2) {
                goto fail;
            }
            break;
        }
        case DUK_REOP_PERIOD: {
            duk_codepoint_t c;
 
            if (sp >= re_ctx->input_end) {
                goto fail;
            }
            c = duk__inp_get_cp(re_ctx, &sp);
            if (duk_unicode_is_line_terminator(c)) {
                /* E5 Sections 15.10.2.8, 7.3 */
                goto fail;
            }
            break;
        }
        case DUK_REOP_RANGES:
        case DUK_REOP_INVRANGES: {
            duk_uint32_t n;
            duk_codepoint_t c;
            duk_small_int_t match;
 
            n = duk__bc_get_u32(re_ctx, &pc);
            if (sp >= re_ctx->input_end) {
                goto fail;
            }
            c = duk__inp_get_cp(re_ctx, &sp);
 
            match = 0;
            while (n) {
                duk_codepoint_t r1, r2;
                r1 = (duk_codepoint_t) duk__bc_get_u32(re_ctx, &pc);
                r2 = (duk_codepoint_t) duk__bc_get_u32(re_ctx, &pc);
                DUK_DDD(DUK_DDDPRINT("matching ranges/invranges, n=%ld, r1=%ld, r2=%ld, c=%ld",
                                     (long) n, (long) r1, (long) r2, (long) c));
                if (c >= r1 && c <= r2) {
                    /* Note: don't bail out early, we must read all the ranges from
                     * bytecode.  Another option is to skip them efficiently after
                     * breaking out of here.  Prefer smallest code.
                     */
                    match = 1;
                }
                n--;
            }
 
            if (op == DUK_REOP_RANGES) {
                if (!match) {
                    goto fail;
                }
            } else {
                DUK_ASSERT(op == DUK_REOP_INVRANGES);
                if (match) {
                    goto fail;
                }
            }
            break;
        }
        case DUK_REOP_ASSERT_START: {
            duk_codepoint_t c;
 
            if (sp <= re_ctx->input) {
                break;
            }
            if (!(re_ctx->re_flags & DUK_RE_FLAG_MULTILINE)) {
                goto fail;
            }
            c = duk__inp_get_prev_cp(re_ctx, sp);
            if (duk_unicode_is_line_terminator(c)) {
                /* E5 Sections 15.10.2.8, 7.3 */
                break;
            }
            goto fail;
        }
        case DUK_REOP_ASSERT_END: {
            duk_codepoint_t c;
            const duk_uint8_t *tmp_sp;
 
            if (sp >= re_ctx->input_end) {
                break;
            }
            if (!(re_ctx->re_flags & DUK_RE_FLAG_MULTILINE)) {
                goto fail;
            }
            tmp_sp = sp;
            c = duk__inp_get_cp(re_ctx, &tmp_sp);
            if (duk_unicode_is_line_terminator(c)) {
                /* E5 Sections 15.10.2.8, 7.3 */
                break;
            }
            goto fail;
        }
        case DUK_REOP_ASSERT_WORD_BOUNDARY:
        case DUK_REOP_ASSERT_NOT_WORD_BOUNDARY: {
            /*
             *  E5 Section 15.10.2.6.  The previous and current character
             *  should -not- be canonicalized as they are now.  However,
             *  canonicalization does not affect the result of IsWordChar()
             *  (which depends on Unicode characters never canonicalizing
             *  into ASCII characters) so this does not matter.
             */
            duk_small_int_t w1, w2;
 
            if (sp <= re_ctx->input) {
                w1 = 0;  /* not a wordchar */
            } else {
                duk_codepoint_t c;
                c = duk__inp_get_prev_cp(re_ctx, sp);
                w1 = duk_unicode_re_is_wordchar(c);
            }
            if (sp >= re_ctx->input_end) {
                w2 = 0;  /* not a wordchar */
            } else {
                const duk_uint8_t *tmp_sp = sp;  /* dummy so sp won't get updated */
                duk_codepoint_t c;
                c = duk__inp_get_cp(re_ctx, &tmp_sp);
                w2 = duk_unicode_re_is_wordchar(c);
            }
 
            if (op == DUK_REOP_ASSERT_WORD_BOUNDARY) {
                if (w1 == w2) {
                    goto fail;
                }
            } else {
                DUK_ASSERT(op == DUK_REOP_ASSERT_NOT_WORD_BOUNDARY);
                if (w1 != w2) {
                    goto fail;
                }
            }
            break;
        }
        case DUK_REOP_JUMP: {
            duk_int32_t skip;
 
            skip = duk__bc_get_i32(re_ctx, &pc);
            pc += skip;
            break;
        }
        case DUK_REOP_SPLIT1: {
            /* split1: prefer direct execution (no jump) */
            const duk_uint8_t *sub_sp;
            duk_int32_t skip;
 
            skip = duk__bc_get_i32(re_ctx, &pc);
            sub_sp = duk__match_regexp(re_ctx, pc, sp);
            if (sub_sp) {
                sp = sub_sp;
                goto match;
            }
            pc += skip;
            break;
        }
        case DUK_REOP_SPLIT2: {
            /* split2: prefer jump execution (not direct) */
            const duk_uint8_t *sub_sp;
            duk_int32_t skip;
 
            skip = duk__bc_get_i32(re_ctx, &pc);
            sub_sp = duk__match_regexp(re_ctx, pc + skip, sp);
            if (sub_sp) {
                sp = sub_sp;
                goto match;
            }
            break;
        }
        case DUK_REOP_SQMINIMAL: {
            duk_uint32_t q, qmin, qmax;
            duk_int32_t skip;
            const duk_uint8_t *sub_sp;
 
            qmin = duk__bc_get_u32(re_ctx, &pc);
            qmax = duk__bc_get_u32(re_ctx, &pc);
            skip = duk__bc_get_i32(re_ctx, &pc);
            DUK_DDD(DUK_DDDPRINT("minimal quantifier, qmin=%lu, qmax=%lu, skip=%ld",
                                 (unsigned long) qmin, (unsigned long) qmax, (long) skip));
 
            q = 0;
            while (q <= qmax) {
                if (q >= qmin) {
                    sub_sp = duk__match_regexp(re_ctx, pc + skip, sp);
                    if (sub_sp) {
                        sp = sub_sp;
                        goto match;
                    }
                }
                sub_sp = duk__match_regexp(re_ctx, pc, sp);
                if (!sub_sp) {
                    break;
                }
                sp = sub_sp;
                q++;
            }
            goto fail;
        }
        case DUK_REOP_SQGREEDY: {
            duk_uint32_t q, qmin, qmax, atomlen;
            duk_int32_t skip;
            const duk_uint8_t *sub_sp;
 
            qmin = duk__bc_get_u32(re_ctx, &pc);
            qmax = duk__bc_get_u32(re_ctx, &pc);
            atomlen = duk__bc_get_u32(re_ctx, &pc);
            skip = duk__bc_get_i32(re_ctx, &pc);
            DUK_DDD(DUK_DDDPRINT("greedy quantifier, qmin=%lu, qmax=%lu, atomlen=%lu, skip=%ld",
                                 (unsigned long) qmin, (unsigned long) qmax, (unsigned long) atomlen, (long) skip));
 
            q = 0;
            while (q < qmax) {
                sub_sp = duk__match_regexp(re_ctx, pc, sp);
                if (!sub_sp) {
                    break;
                }
                sp = sub_sp;
                q++;
            }
            while (q >= qmin) {
                sub_sp = duk__match_regexp(re_ctx, pc + skip, sp);
                if (sub_sp) {
                    sp = sub_sp;
                    goto match;
                }
                if (q == qmin) {
                    break;
                }
 
                /* Note: if atom were to contain e.g. captures, we would need to
                 * re-match the atom to get correct captures.  Simply quantifiers
                 * do not allow captures in their atom now, so this is not an issue.
                 */
 
                DUK_DDD(DUK_DDDPRINT("greedy quantifier, backtrack %ld characters (atomlen)",
                                     (long) atomlen));
                sp = duk__inp_backtrack(re_ctx, &sp, (duk_uint_fast32_t) atomlen);
                q--;
            }
            goto fail;
        }
        case DUK_REOP_SAVE: {
            duk_uint32_t idx;
            const duk_uint8_t *old;
            const duk_uint8_t *sub_sp;
 
            idx = duk__bc_get_u32(re_ctx, &pc);
            if (idx >= re_ctx->nsaved) {
                /* idx is unsigned, < 0 check is not necessary */
                DUK_D(DUK_DPRINT("internal error, regexp save index insane: idx=%ld", (long) idx));
                goto internal_error;
            }
            old = re_ctx->saved[idx];
            re_ctx->saved[idx] = sp;
            sub_sp = duk__match_regexp(re_ctx, pc, sp);
            if (sub_sp) {
                sp = sub_sp;
                goto match;
            }
            re_ctx->saved[idx] = old;
            goto fail;
        }
        case DUK_REOP_WIPERANGE: {
            /* Wipe capture range and save old values for backtracking.
             *
             * XXX: this typically happens with a relatively small idx_count.
             * It might be useful to handle cases where the count is small
             * (say <= 8) by saving the values in stack instead.  This would
             * reduce memory churn and improve performance, at the cost of a
             * slightly higher code footprint.
             */
            duk_uint32_t idx_start, idx_count;
#ifdef DUK_USE_EXPLICIT_NULL_INIT
            duk_uint32_t idx_end, idx;
#endif
            duk_uint8_t **range_save;
            const duk_uint8_t *sub_sp;
 
            idx_start = duk__bc_get_u32(re_ctx, &pc);
            idx_count = duk__bc_get_u32(re_ctx, &pc);
            DUK_DDD(DUK_DDDPRINT("wipe saved range: start=%ld, count=%ld -> [%ld,%ld] (captures [%ld,%ld])",
                                 (long) idx_start, (long) idx_count,
                                 (long) idx_start, (long) (idx_start + idx_count - 1),
                                 (long) (idx_start / 2), (long) ((idx_start + idx_count - 1) / 2)));
            if (idx_start + idx_count > re_ctx->nsaved || idx_count == 0) {
                /* idx is unsigned, < 0 check is not necessary */
                DUK_D(DUK_DPRINT("internal error, regexp wipe indices insane: idx_start=%ld, idx_count=%ld",
                                 (long) idx_start, (long) idx_count));
                goto internal_error;
            }
            DUK_ASSERT(idx_count > 0);
 
            duk_require_stack((duk_context *) re_ctx->thr, 1);
            range_save = (duk_uint8_t **) duk_push_fixed_buffer((duk_context *) re_ctx->thr,
                                                                sizeof(duk_uint8_t *) * idx_count);
            DUK_ASSERT(range_save != NULL);
            DUK_MEMCPY(range_save, re_ctx->saved + idx_start, sizeof(duk_uint8_t *) * idx_count);
#ifdef DUK_USE_EXPLICIT_NULL_INIT
            idx_end = idx_start + idx_count;
            for (idx = idx_start; idx < idx_end; idx++) {
                re_ctx->saved[idx] = NULL;
            }
#else
            DUK_MEMZERO((void *) (re_ctx->saved + idx_start), sizeof(duk_uint8_t *) * idx_count);
#endif
 
            sub_sp = duk__match_regexp(re_ctx, pc, sp);
            if (sub_sp) {
                /* match: keep wiped/resaved values */
                DUK_DDD(DUK_DDDPRINT("match: keep wiped/resaved values [%ld,%ld] (captures [%ld,%ld])",
                                     (long) idx_start, (long) (idx_start + idx_count - 1),
                                         (long) (idx_start / 2), (long) ((idx_start + idx_count - 1) / 2)));
                duk_pop((duk_context *) re_ctx->thr);
                sp = sub_sp;
                goto match;
            }
 
            /* fail: restore saves */
            DUK_DDD(DUK_DDDPRINT("fail: restore wiped/resaved values [%ld,%ld] (captures [%ld,%ld])",
                                 (long) idx_start, (long) (idx_start + idx_count - 1),
                                 (long) (idx_start / 2), (long) ((idx_start + idx_count - 1) / 2)));
            DUK_MEMCPY((void *) (re_ctx->saved + idx_start),
                       (const void *) range_save,
                       sizeof(duk_uint8_t *) * idx_count);
            duk_pop((duk_context *) re_ctx->thr);
            goto fail;
        }
        case DUK_REOP_LOOKPOS:
        case DUK_REOP_LOOKNEG: {
            /*
             *  Needs a save of multiple saved[] entries depending on what range
             *  may be overwritten.  Because the regexp parser does no such analysis,
             *  we currently save the entire saved array here.  Lookaheads are thus
             *  a bit expensive.  Note that the saved array is not needed for just
             *  the lookahead sub-match, but for the matching of the entire sequel.
             *
             *  The temporary save buffer is pushed on to the valstack to handle
             *  errors correctly.  Each lookahead causes a C recursion and pushes
             *  more stuff on the value stack.  If the C recursion limit is less
             *  than the value stack spare, there is no need to check the stack.
             *  We do so regardless, just in case.
             */
 
            duk_int32_t skip;
            duk_uint8_t **full_save;
            const duk_uint8_t *sub_sp;
 
            DUK_ASSERT(re_ctx->nsaved > 0);
 
            duk_require_stack((duk_context *) re_ctx->thr, 1);
            full_save = (duk_uint8_t **) duk_push_fixed_buffer((duk_context *) re_ctx->thr,
                                                               sizeof(duk_uint8_t *) * re_ctx->nsaved);
            DUK_ASSERT(full_save != NULL);
            DUK_MEMCPY(full_save, re_ctx->saved, sizeof(duk_uint8_t *) * re_ctx->nsaved);
 
            skip = duk__bc_get_i32(re_ctx, &pc);
            sub_sp = duk__match_regexp(re_ctx, pc, sp);
            if (op == DUK_REOP_LOOKPOS) {
                if (!sub_sp) {
                    goto lookahead_fail;
                }
            } else {
                if (sub_sp) {
                    goto lookahead_fail;
                }
            }
            sub_sp = duk__match_regexp(re_ctx, pc + skip, sp);
            if (sub_sp) {
                /* match: keep saves */
                duk_pop((duk_context *) re_ctx->thr);
                sp = sub_sp;
                goto match;
            }
 
            /* fall through */
 
         lookahead_fail:
            /* fail: restore saves */
            DUK_MEMCPY((void *) re_ctx->saved,
                       (const void *) full_save,
                       sizeof(duk_uint8_t *) * re_ctx->nsaved);
            duk_pop((duk_context *) re_ctx->thr);
            goto fail;
        }
        case DUK_REOP_BACKREFERENCE: {
            /*
             *  Byte matching for back-references would be OK in case-
             *  sensitive matching.  In case-insensitive matching we need
             *  to canonicalize characters, so back-reference matching needs
             *  to be done with codepoints instead.  So, we just decode
             *  everything normally here, too.
             *
             *  Note: back-reference index which is 0 or higher than
             *  NCapturingParens (= number of capturing parens in the
             *  -entire- regexp) is a compile time error.  However, a
             *  backreference referring to a valid capture which has
             *  not matched anything always succeeds!  See E5 Section
             *  15.10.2.9, step 5, sub-step 3.
             */
            duk_uint32_t idx;
            const duk_uint8_t *p;
 
            idx = duk__bc_get_u32(re_ctx, &pc);
            idx = idx << 1;  /* backref n -> saved indices [n*2, n*2+1] */
            if (idx < 2 || idx + 1 >= re_ctx->nsaved) {
                /* regexp compiler should catch these */
                DUK_D(DUK_DPRINT("internal error, backreference index insane"));
                goto internal_error;
            }
            if (!re_ctx->saved[idx] || !re_ctx->saved[idx+1]) {
                /* capture is 'undefined', always matches! */
                DUK_DDD(DUK_DDDPRINT("backreference: saved[%ld,%ld] not complete, always match",
                                     (long) idx, (long) (idx + 1)));
                break;
            }
            DUK_DDD(DUK_DDDPRINT("backreference: match saved[%ld,%ld]", (long) idx, (long) (idx + 1)));
 
            p = re_ctx->saved[idx];
            while (p < re_ctx->saved[idx+1]) {
                duk_codepoint_t c1, c2;
 
                /* Note: not necessary to check p against re_ctx->input_end:
                 * the memory access is checked by duk__inp_get_cp(), while
                 * valid compiled regexps cannot write a saved[] entry
                 * which points to outside the string.
                 */
                if (sp >= re_ctx->input_end) {
                    goto fail;
                }
                c1 = duk__inp_get_cp(re_ctx, &p);
                c2 = duk__inp_get_cp(re_ctx, &sp);
                if (c1 != c2) {
                    goto fail;
                }
            }
            break;
        }
        default: {
            DUK_D(DUK_DPRINT("internal error, regexp opcode error: %ld", (long) op));
            goto internal_error;
        }
        }
    }
 
 match:
    re_ctx->recursion_depth--;
    return sp;
 
 fail:
    re_ctx->recursion_depth--;
    return NULL;
 
 internal_error:
    DUK_ERROR_INTERNAL_DEFMSG(re_ctx->thr);
    return NULL;  /* never here */
}
 
/*
 *  Exposed matcher function which provides the semantics of RegExp.prototype.exec().
 *
 *  RegExp.prototype.test() has the same semantics as exec() but does not return the
 *  result object (which contains the matching string and capture groups).  Currently
 *  there is no separate test() helper, so a temporary result object is created and
 *  discarded if test() is needed.  This is intentional, to save code space.
 *
 *  Input stack:  [ ... re_obj input ]
 *  Output stack: [ ... result ]
 */
 
DUK_LOCAL void duk__regexp_match_helper(duk_hthread *thr, duk_small_int_t force_global) {
    duk_context *ctx = (duk_context *) thr;
    duk_re_matcher_ctx re_ctx;
    duk_hobject *h_regexp;
    duk_hstring *h_bytecode;
    duk_hstring *h_input;
    duk_uint8_t *p_buf;
    const duk_uint8_t *pc;
    const duk_uint8_t *sp;
    duk_small_int_t match = 0;
    duk_small_int_t global;
    duk_uint_fast32_t i;
    double d;
    duk_uint32_t char_offset;
 
    DUK_ASSERT(thr != NULL);
    DUK_ASSERT(ctx != NULL);
 
    DUK_DD(DUK_DDPRINT("regexp match: regexp=%!T, input=%!T",
                       (duk_tval *) duk_get_tval(ctx, -2),
                       (duk_tval *) duk_get_tval(ctx, -1)));
 
    /*
     *  Regexp instance check, bytecode check, input coercion.
     *
     *  See E5 Section 15.10.6.
     */
 
    /* TypeError if wrong; class check, see E5 Section 15.10.6 */
    h_regexp = duk_require_hobject_with_class(ctx, -2, DUK_HOBJECT_CLASS_REGEXP);
    DUK_ASSERT(h_regexp != NULL);
    DUK_ASSERT(DUK_HOBJECT_GET_CLASS_NUMBER(h_regexp) == DUK_HOBJECT_CLASS_REGEXP);
    DUK_UNREF(h_regexp);
 
    duk_to_string(ctx, -1);
    h_input = duk_get_hstring(ctx, -1);
    DUK_ASSERT(h_input != NULL);
 
    duk_get_prop_stridx(ctx, -2, DUK_STRIDX_INT_BYTECODE);  /* [ ... re_obj input ] -> [ ... re_obj input bc ] */
    h_bytecode = duk_require_hstring(ctx, -1);  /* no regexp instance should exist without a non-configurable bytecode property */
    DUK_ASSERT(h_bytecode != NULL);
 
    /*
     *  Basic context initialization.
     *
     *  Some init values are read from the bytecode header
     *  whose format is (UTF-8 codepoints):
     *
     *    uint   flags
     *    uint   nsaved (even, 2n+2 where n = num captures)
     */
 
    /* [ ... re_obj input bc ] */
 
    DUK_MEMZERO(&re_ctx, sizeof(re_ctx));
 
    re_ctx.thr = thr;
    re_ctx.input = (const duk_uint8_t *) DUK_HSTRING_GET_DATA(h_input);
    re_ctx.input_end = re_ctx.input + DUK_HSTRING_GET_BYTELEN(h_input);
    re_ctx.bytecode = (const duk_uint8_t *) DUK_HSTRING_GET_DATA(h_bytecode);
    re_ctx.bytecode_end = re_ctx.bytecode + DUK_HSTRING_GET_BYTELEN(h_bytecode);
    re_ctx.saved = NULL;
    re_ctx.recursion_limit = DUK_USE_REGEXP_EXECUTOR_RECLIMIT;
    re_ctx.steps_limit = DUK_RE_EXECUTE_STEPS_LIMIT;
 
    /* read header */
    pc = re_ctx.bytecode;
    re_ctx.re_flags = duk__bc_get_u32(&re_ctx, &pc);
    re_ctx.nsaved = duk__bc_get_u32(&re_ctx, &pc);
    re_ctx.bytecode = pc;
 
    DUK_ASSERT(DUK_RE_FLAG_GLOBAL < 0x10000UL);  /* must fit into duk_small_int_t */
    global = (duk_small_int_t) (force_global | (re_ctx.re_flags & DUK_RE_FLAG_GLOBAL));
 
    DUK_ASSERT(re_ctx.nsaved >= 2);
    DUK_ASSERT((re_ctx.nsaved % 2) == 0);
 
    p_buf = (duk_uint8_t *) duk_push_fixed_buffer(ctx, sizeof(duk_uint8_t *) * re_ctx.nsaved);
    DUK_UNREF(p_buf);
    re_ctx.saved = (const duk_uint8_t **) duk_get_buffer(ctx, -1, NULL);
    DUK_ASSERT(re_ctx.saved != NULL);
 
    /* [ ... re_obj input bc saved_buf ] */
 
#if defined(DUK_USE_EXPLICIT_NULL_INIT)
    for (i = 0; i < re_ctx.nsaved; i++) {
        re_ctx.saved[i] = (duk_uint8_t *) NULL;
    }
#elif defined(DUK_USE_ZERO_BUFFER_DATA)
    /* buffer is automatically zeroed */
#else
    DUK_MEMZERO((void *) p_buf, sizeof(duk_uint8_t *) * re_ctx.nsaved);
#endif
 
    DUK_DDD(DUK_DDDPRINT("regexp ctx initialized, flags=0x%08lx, nsaved=%ld, recursion_limit=%ld, steps_limit=%ld",
                         (unsigned long) re_ctx.re_flags, (long) re_ctx.nsaved, (long) re_ctx.recursion_limit,
                         (long) re_ctx.steps_limit));
 
    /*
     *  Get starting character offset for match, and initialize 'sp' based on it.
     *
     *  Note: lastIndex is non-configurable so it must be present (we check the
     *  internal class of the object above, so we know it is).  User code can set
     *  its value to an arbitrary (garbage) value though; E5 requires that lastIndex
     *  be coerced to a number before using.  The code below works even if the
     *  property is missing: the value will then be coerced to zero.
     *
     *  Note: lastIndex may be outside Uint32 range even after ToInteger() coercion.
     *  For instance, ToInteger(+Infinity) = +Infinity.  We track the match offset
     *  as an integer, but pre-check it to be inside the 32-bit range before the loop.
     *  If not, the check in E5 Section 15.10.6.2, step 9.a applies.
     */
 
    /* XXX: lastIndex handling produces a lot of asm */
 
    /* [ ... re_obj input bc saved_buf ] */
 
    duk_get_prop_stridx(ctx, -4, DUK_STRIDX_LAST_INDEX);  /* -> [ ... re_obj input bc saved_buf lastIndex ] */
    (void) duk_to_int(ctx, -1);  /* ToInteger(lastIndex) */
    d = duk_get_number(ctx, -1);  /* integer, but may be +/- Infinite, +/- zero (not NaN, though) */
    duk_pop(ctx);
 
    if (global) {
        if (d < 0.0 || d > (double) DUK_HSTRING_GET_CHARLEN(h_input)) {
            /* match fail */
            char_offset = 0;   /* not really necessary */
            DUK_ASSERT(match == 0);
            goto match_over;
        }
        char_offset = (duk_uint32_t) d;
    } else {
        /* lastIndex must be ignored for non-global regexps, but get the
         * value for (theoretical) side effects.  No side effects can
         * really occur, because lastIndex is a normal property and is
         * always non-configurable for RegExp instances.
         */
        char_offset = (duk_uint32_t) 0;
    }
 
    sp = re_ctx.input + duk_heap_strcache_offset_char2byte(thr, h_input, char_offset);
 
    /*
     *  Match loop.
     *
     *  Try matching at different offsets until match found or input exhausted.
     */
 
    /* [ ... re_obj input bc saved_buf ] */
 
    DUK_ASSERT(match == 0);
 
    for (;;) {
        /* char offset in [0, h_input->clen] (both ends inclusive), checked before entry */
        DUK_ASSERT_DISABLE(char_offset >= 0);
        DUK_ASSERT(char_offset <= DUK_HSTRING_GET_CHARLEN(h_input));
 
        /* Note: ctx.steps is intentionally not reset, it applies to the entire unanchored match */
        DUK_ASSERT(re_ctx.recursion_depth == 0);
 
        DUK_DDD(DUK_DDDPRINT("attempt match at char offset %ld; %p [%p,%p]",
                             (long) char_offset, (const void *) sp,
                             (const void *) re_ctx.input, (const void *) re_ctx.input_end));
 
        /*
         *  Note:
         *
         *    - duk__match_regexp() is required not to longjmp() in ordinary "non-match"
         *      conditions; a longjmp() will terminate the entire matching process.
         *
         *    - Clearing saved[] is not necessary because backtracking does it
         *
         *    - Backtracking also rewinds ctx.recursion back to zero, unless an
         *      internal/limit error occurs (which causes a longjmp())
         *
         *    - If we supported anchored matches, we would break out here
         *      unconditionally; however, Ecmascript regexps don't have anchored
         *      matches.  It might make sense to implement a fast bail-out if
         *      the regexp begins with '^' and sp is not 0: currently we'll just
         *      run through the entire input string, trivially failing the match
         *      at every non-zero offset.
         */
 
        if (duk__match_regexp(&re_ctx, re_ctx.bytecode, sp) != NULL) {
            DUK_DDD(DUK_DDDPRINT("match at offset %ld", (long) char_offset));
            match = 1;
            break;
        }
 
        /* advance by one character (code point) and one char_offset */
        char_offset++;
        if (char_offset > DUK_HSTRING_GET_CHARLEN(h_input)) {
            /*
             *  Note:
             *
             *    - Intentionally attempt (empty) match at char_offset == k_input->clen
             *
             *    - Negative char_offsets have been eliminated and char_offset is duk_uint32_t
             *      -> no need or use for a negative check
             */
 
            DUK_DDD(DUK_DDDPRINT("no match after trying all sp offsets"));
            break;
        }
 
        /* avoid calling at end of input, will DUK_ERROR (above check suffices to avoid this) */
        (void) duk__utf8_advance(thr, &sp, re_ctx.input, re_ctx.input_end, (duk_uint_fast32_t) 1);
    }
 
 match_over:
 
    /*
     *  Matching complete, create result array or return a 'null'.  Update lastIndex
     *  if necessary.  See E5 Section 15.10.6.2.
     *
     *  Because lastIndex is a character (not byte) offset, we need the character
     *  length of the match which we conveniently get as a side effect of interning
     *  the matching substring (0th index of result array).
     *
     *  saved[0]         start pointer (~ byte offset) of current match
     *  saved[1]         end pointer (~ byte offset) of current match (exclusive)
     *  char_offset      start character offset of current match (-> .index of result)
     *  char_end_offset  end character offset (computed below)
     */
 
    /* [ ... re_obj input bc saved_buf ] */
 
    if (match) {
#ifdef DUK_USE_ASSERTIONS
        duk_hobject *h_res;
#endif
        duk_uint32_t char_end_offset = 0;
 
        DUK_DDD(DUK_DDDPRINT("regexp matches at char_offset %ld", (long) char_offset));
 
        DUK_ASSERT(re_ctx.nsaved >= 2);        /* must have start and end */
        DUK_ASSERT((re_ctx.nsaved % 2) == 0);  /* and even number */
 
        /* XXX: Array size is known before and (2 * re_ctx.nsaved) but not taken
         * advantage of now.  The array is not compacted either, as regexp match
         * objects are usually short lived.
         */
 
        duk_push_array(ctx);
 
#ifdef DUK_USE_ASSERTIONS
        h_res = duk_require_hobject(ctx, -1);
        DUK_ASSERT(DUK_HOBJECT_HAS_EXTENSIBLE(h_res));
        DUK_ASSERT(DUK_HOBJECT_HAS_EXOTIC_ARRAY(h_res));
        DUK_ASSERT(DUK_HOBJECT_GET_CLASS_NUMBER(h_res) == DUK_HOBJECT_CLASS_ARRAY);
#endif
 
        /* [ ... re_obj input bc saved_buf res_obj ] */
 
        duk_push_u32(ctx, char_offset);
        duk_xdef_prop_stridx_wec(ctx, -2, DUK_STRIDX_INDEX);
 
        duk_dup(ctx, -4);
        duk_xdef_prop_stridx_wec(ctx, -2, DUK_STRIDX_INPUT);
 
        for (i = 0; i < re_ctx.nsaved; i += 2) {
            /* Captures which are undefined have NULL pointers and are returned
             * as 'undefined'.  The same is done when saved[] pointers are insane
             * (this should, of course, never happen in practice).
             */
            if (re_ctx.saved[i] && re_ctx.saved[i+1] && re_ctx.saved[i+1] >= re_ctx.saved[i]) {
                duk_hstring *h_saved;
 
                duk_push_lstring(ctx,
                                 (const char *) re_ctx.saved[i],
                                 (duk_size_t) (re_ctx.saved[i+1] - re_ctx.saved[i]));
                h_saved = duk_get_hstring(ctx, -1);
                DUK_ASSERT(h_saved != NULL);
 
                if (i == 0) {
                    /* Assumes that saved[0] and saved[1] are always
                     * set by regexp bytecode (if not, char_end_offset
                     * will be zero).  Also assumes clen reflects the
                     * correct char length.
                     */
                    char_end_offset = char_offset + DUK_HSTRING_GET_CHARLEN(h_saved);
                }
            } else {
                duk_push_undefined(ctx);
            }
 
            /* [ ... re_obj input bc saved_buf res_obj val ] */
            duk_put_prop_index(ctx, -2, i / 2);
        }
 
        /* [ ... re_obj input bc saved_buf res_obj ] */
 
        /* NB: 'length' property is automatically updated by the array setup loop */
 
        if (global) {
            /* global regexp: lastIndex updated on match */
            duk_push_u32(ctx, char_end_offset);
            duk_put_prop_stridx(ctx, -6, DUK_STRIDX_LAST_INDEX);
        } else {
            /* non-global regexp: lastIndex never updated on match */
            ;
        }
    } else {
        /*
         *  No match, E5 Section 15.10.6.2, step 9.a.i - 9.a.ii apply, regardless
         *  of 'global' flag of the RegExp.  In particular, if lastIndex is invalid
         *  initially, it is reset to zero.
         */
 
        DUK_DDD(DUK_DDDPRINT("regexp does not match"));
 
        duk_push_null(ctx);
 
        /* [ ... re_obj input bc saved_buf res_obj ] */
 
        duk_push_int(ctx, 0);
        duk_put_prop_stridx(ctx, -6, DUK_STRIDX_LAST_INDEX);
    }
 
    /* [ ... re_obj input bc saved_buf res_obj ] */
 
    duk_insert(ctx, -5);
 
    /* [ ... res_obj re_obj input bc saved_buf ] */
 
    duk_pop_n(ctx, 4);
 
    /* [ ... res_obj ] */
 
    /* XXX: these last tricks are unnecessary if the function is made
     * a genuine native function.
     */
}
 
DUK_INTERNAL void duk_regexp_match(duk_hthread *thr) {
    duk__regexp_match_helper(thr, 0 /*force_global*/);
}
 
/* This variant is needed by String.prototype.split(); it needs to perform
 * global-style matching on a cloned RegExp which is potentially non-global.
 */
DUK_INTERNAL void duk_regexp_match_force_global(duk_hthread *thr) {
    duk__regexp_match_helper(thr, 1 /*force_global*/);
}
 
#else  /* DUK_USE_REGEXP_SUPPORT */
 
/* regexp support disabled */
 
#endif  /* DUK_USE_REGEXP_SUPPORT */