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ext/bcmath: Use SIMD for trailing zero counts during conversion (#14166)

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Changed to count trailing zeros using SIMD when converting a string to
a bc_num structure if possible.

Removed unnecessary pointer resetting.

Added UNEXPECTED to some branches.
This commit is contained in:
Saki Takamachi
2024-05-09 19:23:59 +09:00
committed by GitHub
parent 6e7adb3c48
commit 1a3d870c1e
1 changed files with 34 additions and 9 deletions
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43
ext/bcmath/libbcmath/src/str2num.c
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@@ -76,6 +76,35 @@ static const char *bc_count_digits(const char *str, const char *end)
return str;
}
static inline const char *bc_skip_zero_reverse(const char *scanner, const char *stop)
{
/* Check in bulk */
#ifdef __SSE2__
const __m128i c_zero_repeat = _mm_set1_epi8('0');
while (scanner - sizeof(__m128i) >= stop) {
scanner -= sizeof(__m128i);
__m128i bytes = _mm_loadu_si128((const __m128i *) scanner);
/* Checks if all numeric strings are equal to '0'. */
bytes = _mm_cmpeq_epi8(bytes, c_zero_repeat);
int mask = _mm_movemask_epi8(bytes);
/* The probability of having 16 trailing 0s in a row is very low, so we use EXPECTED. */
if (EXPECTED(mask != 0xffff)) {
/* Move the pointer back and check each character in loop. */
scanner += sizeof(__m128i);
break;
}
}
#endif
/* Exclude trailing zeros. */
while (scanner - 1 >= stop && scanner[-1] == '0') {
scanner--;
}
return scanner;
}
/* Assumes `num` points to NULL, i.e. does yet not hold a number. */
bool bc_str2num(bc_num *num, const char *str, const char *end, size_t scale, bool auto_scale)
{
@@ -104,7 +133,7 @@ bool bc_str2num(bc_num *num, const char *str, const char *end, size_t scale, boo
const char *decimal_point = (*ptr == '.') ? ptr : NULL;
/* If a non-digit and non-decimal-point indicator is in the string, i.e. an invalid character */
if (!decimal_point && *ptr != '\0') {
if (UNEXPECTED(!decimal_point && *ptr != '\0')) {
goto fail;
}
@@ -112,24 +141,20 @@ bool bc_str2num(bc_num *num, const char *str, const char *end, size_t scale, boo
if (decimal_point) {
/* search */
fractional_ptr = fractional_end = decimal_point + 1;
if (*fractional_ptr == '\0') {
/* For strings that end with a decimal point, such as "012." */
if (UNEXPECTED(*fractional_ptr == '\0')) {
goto after_fractional;
}
/* validate */
fractional_end = bc_count_digits(fractional_ptr, end);
if (*fractional_end != '\0') {
if (UNEXPECTED(*fractional_end != '\0')) {
/* invalid num */
goto fail;
}
/* Exclude trailing zeros. */
while (fractional_end - 1 > decimal_point && fractional_end[-1] == '0') {
fractional_end--;
}
/* Move the pointer to the beginning of the fraction. */
fractional_ptr = decimal_point + 1;
fractional_end = bc_skip_zero_reverse(fractional_end, fractional_ptr);
/* Calculate the length of the fraction excluding trailing zero. */
str_scale = fractional_end - fractional_ptr;