+char *
+cistrstr(const char *s, const char *sub) {
+ int c, csub;
+ unsigned int len;
+
+ if(!sub)
+ return (char *)s;
+ if((c = *sub++) != 0) {
+ c = tolower(c);
+ len = strlen(sub);
+ do {
+ do {
+ if((csub = *s++) == 0)
+ return (NULL);
+ }
+ while(tolower(csub) != c);
+ }
+ while(strncasecmp(s, sub, len) != 0);
+ s--;
+ }
+ return (char *)s;
+}
+