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wcsfilecmp: Stop actually computing the numbers

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This just compares two longs as strings on the go.

We can simply

1. ignore leading zeroes - they have no influence on the value
2. compare the digits char-by-char
3. keep the comparison for the first differing digit
4. if one number is longer than the other, that is larger
5. if the numbers have the same length, the one larger in the first
differing digit is larger

This makes this comparison quite a bit faster, which makes globs in
directories with numbered files up to 20% faster.

Note that, for historical reasons, this still ignores whitespace right
after the numbers!
This commit is contained in:
Fabian Homborg 2021-10-07 17:50:07 +02:00
parent 01919f1785
commit 6af3896217
1 changed files with 39 additions and 10 deletions
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49
src/util.cpp
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@ -17,18 +17,47 @@
// Compare the strings to see if they begin with an integer that can be compared and return the
// result of that comparison.
static int wcsfilecmp_leading_digits(const wchar_t **a, const wchar_t **b) {
const wchar_t *a_end, *b_end;
const wchar_t *a1 = *a;
const wchar_t *b1 = *b;
long a_num = fish_wcstol(*a, &a_end, 10);
if (errno > 0) return 0; // invalid number -- fallback to simple string compare
long b_num = fish_wcstol(*b, &b_end, 10);
if (errno > 0) return 0; // invalid number -- fallback to simple string compare
// Ignore leading 0s.
while (*a1 == L'0') a1++;
while (*b1 == L'0') b1++;
if (a_num < b_num) return -1;
if (a_num > b_num) return 1;
*a = a_end;
*b = b_end;
return 0;
int ret = 0;
while (true) {
if (iswdigit(*a1) && iswdigit(*b1)) {
// We keep the cmp value for the
// first differing digit.
//
// If the numbers have the same length, that's the value.
if (ret == 0) {
// Comparing the string value is the same as numerical
// for wchar_t digits!
if (*a1 > *b1) ret = 1;
if (*b1 > *a1) ret = -1;
}
} else {
// We don't have negative numbers and we only allow ints,
// and we have already skipped leading zeroes,
// so the longer number is larger automatically.
if (iswdigit(*a1)) ret = 1;
if (iswdigit(*b1)) ret = -1;
break;
}
a1++;
b1++;
}
// For historical reasons, we skip trailing whitespace
// like fish_wcstol does!
// This is used in sorting globs, and that's supposed to be stable.
while (iswspace(*a1)) a1++;
while (iswspace(*b1)) b1++;
*a = a1;
*b = b1;
return ret;
}
/// Compare two strings, representing file names, using "natural" ordering. This means that letter