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simpler optimizations

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Signed-off-by: Shikhar <shikharish05@gmail.com>
This commit is contained in:
Shikhar 2026-01-02 02:45:11 +05:30
parent 13d4b94183
commit b14e6a466a
1 changed files with 34 additions and 69 deletions
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103
include/fast_float/ascii_number.h
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@ -32,7 +32,7 @@ template <typename UC> fastfloat_really_inline constexpr bool has_simd_opt() {
// able to optimize it well.
template <typename UC>
fastfloat_really_inline constexpr bool is_integer(UC c) noexcept {
return !(c > UC('9') || c < UC('0'));
return (unsigned)(c - UC('0')) <= 9u;
}
fastfloat_really_inline constexpr uint64_t byteswap(uint64_t val) {
@ -83,11 +83,10 @@ read4_to_u32(UC const *chars) {
uint32_t val;
::memcpy(&val, chars, sizeof(uint32_t));
#if FASTFLOAT_IS_BIG_ENDIAN == 1
val = byteswap(val);
val = byteswap_32(val);
#endif
return val;
}
#ifdef FASTFLOAT_SSE2
fastfloat_really_inline uint64_t simd_read8_to_u64(__m128i const data) {
@ -169,6 +168,11 @@ is_made_of_eight_digits_fast(uint64_t val) noexcept {
0x8080808080808080));
}
fastfloat_really_inline constexpr bool
is_made_of_four_digits_fast(uint32_t val) noexcept {
return !((((val + 0x46464646) | (val - 0x30303030)) & 0x80808080));
}
fastfloat_really_inline FASTFLOAT_CONSTEXPR14 uint32_t
parse_four_digits_unrolled(uint32_t val) noexcept {
val -= 0x30303030;
@ -648,77 +652,38 @@ parse_int_string(UC const *p, UC const *pend, T &value,
return answer;
}
uint32_t digits;
if (len >= 4) {
digits = read4_to_u32(p);
} else {
uint32_t b0 = uint32_t(uint8_t(p[0]));
uint32_t b1 = (len > 1) ? uint32_t(uint8_t(p[1])) : 0xFFu;
uint32_t b2 = (len > 2) ? uint32_t(uint8_t(p[2])) : 0xFFu;
digits = b0 | (b1 << 8) | (b2 << 16) | (0xFFu << 24);
}
uint32_t magic =
((digits + 0x46464646u) | (digits - 0x30303030u)) & 0x80808080u;
uint32_t nd = (magic == 0) ? 4u : (uint32_t(countr_zero_32(magic)) >> 3);
if (nd == 0) {
if (has_leading_zeros) {
value = 0;
uint32_t digits = read4_to_u32(p);
if (is_made_of_four_digits_fast(digits)) {
uint32_t v = parse_four_digits_unrolled(digits);
if (len >= 5 && is_integer(p[4])) {
v = v * 10 + uint32_t(p[4] - '0');
if (len >= 6 && is_integer(p[5])) {
answer.ec = std::errc::result_out_of_range;
const UC *q = p + 5;
while (q != pend && is_integer(*q)) {
q++;
}
answer.ptr = q;
return answer;
}
if (v > 65535) {
answer.ec = std::errc::result_out_of_range;
answer.ptr = p + 5;
return answer;
}
value = uint16_t(v);
answer.ec = std::errc();
answer.ptr = p + 5;
return answer;
}
// 4 digits
value = uint16_t(v);
answer.ec = std::errc();
answer.ptr = p;
return answer;
}
answer.ec = std::errc::invalid_argument;
answer.ptr = first;
return answer;
}
if (nd < 4) {
// mask out non-digit bytes and replace with '0' (0x30)
uint32_t mask = 0xFFFFFFFFu >> ((4u - nd) * 8u);
uint32_t padded = (digits & mask) | (~mask & 0x30303030u);
uint32_t v = parse_four_digits_unrolled(padded);
constexpr uint32_t divs[] = {0, 1000, 100, 10};
value = (uint16_t)(v / divs[nd]);
answer.ec = std::errc();
answer.ptr = p + nd;
return answer;
}
uint32_t v = parse_four_digits_unrolled(digits);
uint32_t d4 = (len > 4) ? uint32_t(p[4] - '0') : 10u;
if (d4 > 9u) {
value = (uint16_t)v;
answer.ec = std::errc();
answer.ptr = p + 4;
return answer;
}
if (len > 5) {
uint32_t d5 = uint32_t(p[5]) - uint32_t('0');
if (d5 <= 9u) {
const UC *q = p + 6;
while (q < pend && uint32_t(*q) - uint32_t('0') <= 9u)
++q;
answer.ec = std::errc::result_out_of_range;
answer.ptr = q;
answer.ptr = p + 4;
return answer;
}
}
// overflow check
if (v > 6553u || (v == 6553u && d4 > 5u)) {
answer.ec = std::errc::result_out_of_range;
answer.ptr = p + 5;
return answer;
}
value = (uint16_t)(v * 10u + d4);
answer.ec = std::errc();
answer.ptr = p + 5;
return answer;
}
}