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Magical optimizations from @aqrit

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This commit is contained in:
Daniel Lemire 2020-11-09 19:06:51 -05:00
parent 8ea46c6155
commit 41ee34701b
1 changed files with 29 additions and 6 deletions
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35
include/fast_float/ascii_number.h
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@ -15,20 +15,43 @@ namespace fast_float {
fastfloat_really_inline bool is_integer(char c) noexcept { return c >= '0' && c <= '9'; }
// credit @aqrit
fastfloat_really_inline uint32_t parse_eight_digits_unrolled(uint64_t val) {
const uint64_t mask = 0x000000FF000000FF;
const uint64_t mul1 = 0x000F424000000064; // 100 + (1000000ULL << 32)
const uint64_t mul2 = 0x0000271000000001; // 1 + (10000ULL << 32)
val -= 0x3030303030303030;
val = (val * 10) + (val >> 8); // val = (val * 2561) >> 8;
val = (((val & mask) * mul1) + (((val >> 16) & mask) * mul2)) >> 32;
return val;
}
// credit: https://johnnylee-sde.github.io/Fast-numeric-string-to-int/
//fastfloat_really_inline uint32_t parse_eight_digits_unrolled(uint64_t val) noexcept {
// uint64_t val;
// ::memcpy(&val, chars, sizeof(uint64_t));
// val = (val & 0x0F0F0F0F0F0F0F0F) * 2561 >> 8;
// val = (val & 0x00FF00FF00FF00FF) * 6553601 >> 16;
// return uint32_t((val & 0x0000FFFF0000FFFF) * 42949672960001 >> 32);
//}
fastfloat_really_inline uint32_t parse_eight_digits_unrolled(const char *chars) noexcept {
uint64_t val;
::memcpy(&val, chars, sizeof(uint64_t));
val = (val & 0x0F0F0F0F0F0F0F0F) * 2561 >> 8;
val = (val & 0x00FF00FF00FF00FF) * 6553601 >> 16;
return uint32_t((val & 0x0000FFFF0000FFFF) * 42949672960001 >> 32);
return parse_eight_digits_unrolled(val);
}
// credit @aqrit
fastfloat_really_inline bool is_made_of_eight_digits_fast(uint64_t val) noexcept {
return (((val & 0xF0F0F0F0F0F0F0F0) |
(((val + 0x0606060606060606) & 0xF0F0F0F0F0F0F0F0) >> 4)) ==
0x3333333333333333);
return !((((val + 0x4646464646464646) | (val - 0x3030303030303030)) &
0x8080808080808080));
}
//fastfloat_really_inline bool is_made_of_eight_digits_fast(uint64_t val) noexcept {
// return (((val & 0xF0F0F0F0F0F0F0F0) |
// (((val + 0x0606060606060606) & 0xF0F0F0F0F0F0F0F0) >> 4)) ==
// 0x3333333333333333);
//}
fastfloat_really_inline bool is_made_of_eight_digits_fast(const char *chars) noexcept {