duk_heap_hashstring.c File Reference

#include "duk_internal.h"

Go to the source code of this file.

Functions
DUK_INTERNAL duk_uint32_t	duk_heap_hashstring (duk_heap *heap, const duk_uint8_t *str, duk_size_t len)

Function Documentation

duk_heap_hashstring()

DUK_INTERNAL duk_uint32_t duk_heap_hashstring	(	duk_heap *	heap,
		const duk_uint8_t *	str,
		duk_size_t	len )

Definition at line 88 of file duktape-1.8.0/src-separate/duk_heap_hashstring.c.

                                                                                                      {
    duk_uint32_t hash;
    duk_size_t step;
    duk_size_t off;
 
    /* Slightly modified "Bernstein hash" from:
     *
     *     http://eternallyconfuzzled.com/tuts/algorithms/jsw_tut_hashing.aspx
     *
     * Modifications: string skipping and reverse direction similar to
     * Lua 5.1.5, and different hash initializer.
     *
     * The reverse direction ensures last byte it always included in the
     * hash which is a good default as changing parts of the string are
     * more often in the suffix than in the prefix.
     */
 
    hash = heap->hash_seed ^ ((duk_uint32_t) len);  /* Bernstein hash init value is normally 5381 */
    step = (len >> DUK_USE_STRHASH_SKIP_SHIFT) + 1;
    for (off = len; off >= step; off -= step) {
        DUK_ASSERT(off >= 1);  /* off >= step, and step >= 1 */
        hash = (hash * 33) + str[off - 1];
    }
 
#if defined(DUK_USE_STRHASH16)
    /* Truncate to 16 bits here, so that a computed hash can be compared
     * against a hash stored in a 16-bit field.
     */
    hash &= 0x0000ffffUL;
#endif
    return hash;
}

References DUK_ASSERT, DUK_USE_STRHASH_SKIP_SHIFT, and duk_heap::hash_seed.