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Improve performance of lit_utf8_string_calc_hash_last_bytes.

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JerryScript-DCO-1.0-Signed-off-by: Evgeny Gavrin e.gavrin@samsung.com
This commit is contained in:
Evgeny Gavrin
2015-08-19 22:26:54 +03:00
parent ccfe1f1cd6
commit e0dee65a36
6 changed files with 82 additions and 86 deletions
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jerry-core/lit/lit-strings.cpp
+33 -13
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@@ -597,28 +597,48 @@ lit_read_code_point_from_utf8 (const lit_utf8_byte_t *buf_p, /**< buffer with ch
return bytes_count;
} /* lit_read_code_point_from_utf8 */
/**
* Calculate hash from last LIT_STRING_HASH_LAST_BYTES_COUNT characters from the buffer.
* Calc hash using the specified hash_basis.
*
* NOTE:
* This is implementation of FNV-1a hash function, which is released into public domain.
* Constants used, are carefully picked primes by the authors.
* More info: http://www.isthe.com/chongo/tech/comp/fnv/
*
* @return ecma-string's hash
*/
lit_string_hash_t
lit_utf8_string_calc_hash_last_bytes (const lit_utf8_byte_t *utf8_buf_p, /**< characters buffer */
lit_utf8_size_t utf8_buf_size) /**< number of characters in the buffer */
lit_string_hash_t __attr_always_inline___
lit_utf8_string_hash_combine (lit_string_hash_t hash_basis, /**< hash to be combined with */
const lit_utf8_byte_t *utf8_buf_p, /**< characters buffer */
lit_utf8_size_t utf8_buf_size) /**< number of characters in the buffer */
{
JERRY_ASSERT (utf8_buf_p != NULL || utf8_buf_size == 0);
lit_utf8_byte_t byte1 = (utf8_buf_size > 0) ? utf8_buf_p[utf8_buf_size - 1] : (lit_utf8_byte_t) 0;
lit_utf8_byte_t byte2 = (utf8_buf_size > 1) ? utf8_buf_p[utf8_buf_size - 2] : (lit_utf8_byte_t) 0;
uint32_t hash = hash_basis;
uint32_t t1 = (uint32_t) byte1 + (uint32_t) byte2;
uint32_t t2 = t1 * 0x24418b66;
uint32_t t3 = (t2 >> 16) ^ (t2 & 0xffffu);
uint32_t t4 = (t3 >> 8) ^ (t3 & 0xffu);
for (uint32_t i = 0; i < utf8_buf_size; i++)
{
// 16777619 is 32 bit FNV_prime = 2^24 + 2^8 + 0x93 = 16777619
hash = (hash ^ utf8_buf_p[i]) * 16777619;
}
return (lit_string_hash_t) t4;
} /* lit_utf8_string_calc_hash_last_bytes */
return (lit_string_hash_t) hash;
} /* lit_utf8_string_hash_combine */
/**
* Calculate hash from the buffer.
*
* @return ecma-string's hash
*/
lit_string_hash_t __attr_always_inline___
lit_utf8_string_calc_hash (const lit_utf8_byte_t *utf8_buf_p, /**< characters buffer */
lit_utf8_size_t utf8_buf_size) /**< number of characters in the buffer */
{
JERRY_ASSERT (utf8_buf_p != NULL || utf8_buf_size == 0);
// 32 bit offset_basis for FNV = 2166136261
return lit_utf8_string_hash_combine ((lit_string_hash_t) 2166136261, utf8_buf_p, utf8_buf_size);
} /* lit_utf8_string_calc_hash */
/**
* Return code unit at the specified position in string