read-cache: add strcmp_offset function

diff --git a/read-cache.c b/read-cache.c
index e44775182392c5672fd6ec84eb954db339e5a1ea..11823f5dbcbe277532d33559c3ff4dd43990c866 100644 (file)
--- a/read-cache.c
+++ b/read-cache.c
@@ -887,6 +887,26 @@ static int has_file_name(struct index_state *istate,
        return retval;
 }
 
+
+/*
+ * Like strcmp(), but also return the offset of the first change.
+ * If strings are equal, return the length.
+ */
+int strcmp_offset(const char *s1, const char *s2, size_t *first_change)
+{
+       size_t k;
+
+       if (!first_change)
+               return strcmp(s1, s2);
+
+       for (k = 0; s1[k] == s2[k]; k++)
+               if (s1[k] == '\0')
+                       break;
+
+       *first_change = k;
+       return (unsigned char)s1[k] - (unsigned char)s2[k];
+}
+
 /*
  * Do we have another file with a pathname that is a proper
  * subset of the name we're trying to add?