src/string/strverscmp.c

#define _GNU_SOURCE
#include <ctype.h>
#include <string.h>

int strverscmp(const char *l0, const char *r0)
{
	const unsigned char *l = (const void *)l0;
	const unsigned char *r = (const void *)r0;
	size_t i, dp, j;
	int z = 1;

	/* Find maximal matching prefix and track its maximal digit
	 * suffix and whether those digits are all zeros. */
	for (dp=i=0; l[i]==r[i]; i++) {
		int c = l[i];
		if (!c) return 0;
		if (!isdigit(c)) dp=i+1, z=1;
		else if (c!='0') z=0;
	}

	if (l[dp]-'1'<9U && r[dp]-'1'<9U) {
		/* If we're looking at non-degenerate digit sequences starting
		 * with nonzero digits, longest digit string is greater. */
		for (j=i; isdigit(l[j]); j++)
			if (!isdigit(r[j])) return 1;
		if (isdigit(r[j])) return -1;
	} else if (z && dp<i && (isdigit(l[i]) || isdigit(r[i]))) {
		/* Otherwise, if common prefix of digit sequence is
		 * all zeros, digits order less than non-digits. */
		return (unsigned char)(l[i]-'0') - (unsigned char)(r[i]-'0');
	}

	return l[i] - r[i];
}