coffee/fast_float
1
0
Fork 0
mirror of https://github.com/fastfloat/fast_float.git synced 2026-06-15 08:26:08 +08:00
Code Issues Packages Projects Releases Wiki Activity

Merge pull request #381 from redis-performance/pr/integer-scan-unroll

Browse Source 
Unroll the integer-part digit scan (straight-line for the common 1-5 digit case)
This commit is contained in:
Daniel Lemire 2026-06-01 13:44:06 -04:00 committed by GitHub
commit 0f682cd6eb
No known key found for this signature in database
GPG Key ID: B5690EEEBB952194
1 changed files with 29 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

27
include/fast_float/ascii_number.h
View File

@ -354,14 +354,37 @@ parse_number_string(UC const *p, UC const *pend,
uint64_t i = 0; // an unsigned int avoids signed overflows (which are bad) uint64_t i = 0; // an unsigned int avoids signed overflows (which are bad)
// Straight-line unroll of the integer-part scan: most integer parts are
// 1-5 digits, so peeling the first iterations eliminates the loop back-edge
// for the common case. Semantics are identical to the original `while` loop:
// i = 10*i + digit, advancing p.
if ((p != pend) && is_integer(*p)) {
i = uint64_t(*p - UC('0'));
++p;
if ((p != pend) && is_integer(*p)) {
i = 10 * i + uint64_t(*p - UC('0'));
++p;
if ((p != pend) && is_integer(*p)) {
i = 10 * i + uint64_t(*p - UC('0'));
++p;
if ((p != pend) && is_integer(*p)) {
i = 10 * i + uint64_t(*p - UC('0'));
++p;
if ((p != pend) && is_integer(*p)) {
i = 10 * i + uint64_t(*p - UC('0'));
++p;
while ((p != pend) && is_integer(*p)) { while ((p != pend) && is_integer(*p)) {
// a multiplication by 10 is cheaper than an arbitrary integer // a multiplication by 10 is cheaper than an arbitrary integer
// multiplication // multiplication
i = 10 * i + i = 10 * i +
uint64_t(*p - uint64_t(*p - UC('0')); // might overflow, handled later
UC('0')); // might overflow, we will handle the overflow later
++p; ++p;
} }
}
}
}
}
}
UC const *const end_of_integer_part = p; UC const *const end_of_integer_part = p;
int64_t digit_count = int64_t(end_of_integer_part - start_digits); int64_t digit_count = int64_t(end_of_integer_part - start_digits);
answer.integer = span<UC const>(start_digits, size_t(digit_count)); answer.integer = span<UC const>(start_digits, size_t(digit_count));