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grok_bin_oct_dec: Speed up overflow detection

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We can compute outside the loop the exact value at which the next
iteration wil overflow, saving some operations
This commit is contained in:
Karl Williamson 2025-11-30 14:31:52 -07:00 committed by Karl Williamson
parent 628a2f68b9
commit f7d9d8b9ab
1 changed files with 5 additions and 9 deletions
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14
numeric.c
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@ -465,6 +465,9 @@ Perl_grok_bin_oct_hex(pTHX_ const char * const start,
NV value_nv = 0;
const PERL_UINT_FAST8_T base = 1 << shift; /* 2, 8, or 16 */
/* Value above which, the next digit processed would overflow */
UV max_div = UV_MAX >> shift;
for (; s < e; s++) {
if (generic_isCC_(*s, class_bit)) {
/* Write it in this wonky order with a goto to attempt to get the
@ -473,19 +476,12 @@ Perl_grok_bin_oct_hex(pTHX_ const char * const start,
(khw suspects that adding a LIKELY() just above would do the
same thing) */
redo: ;
/* Make room for the next digit */
UV tentative_value = value << shift;
/* If shiftng back doesn't yield the previous value, it was
* because a bit got shifted off the left end, so overflowed.
* But if it worked, add the new digit. */
if (LIKELY((tentative_value >> shift) == value)) {
if (LIKELY(value <= max_div)) {
/* Note XDIGIT_VALUE() is branchless, works on binary and
* octal as well, so can be used here, without noticeably
* slowing those down (it does have unnecessary shifts, ANDSs,
* and additions for those) */
value = tentative_value | XDIGIT_VALUE(*s);
value = (value << shift) | XDIGIT_VALUE(*s);
factor *= base;
continue;
}