`ls`/checks.h: move `startsWith*` functions to header.

i figure these'll be useful in other programs, so might as well go ahead and add them.

lib/checks.h

@@ -0,0 +1,26 @@
+#include <stdbool.h>
+#include <string.h>
+
+static bool startsWithChar(const char *pre, const char str) {
+  char *e;
+  int index;
+  e = strchr(pre, str);
+  index = (int)(e - pre);
+  return index == 0;
+}
+
+static bool startsWithStr(char *prefix, char *string) {
+  if (strlen(prefix) > strlen(string)) {
+    return false;
+  }
+  int max = strlen(prefix);
+  int i = 0;
+  do {
+    if (prefix[i] == string[i]) {
+      i++;
+    } else {
+      return false;
+    }
+  } while (i < max);
+  return true;
+}

src/ls.c

@@ -8,6 +8,7 @@
 
 #include "ansi-colour.h"
 #include "file.h"
+#include "checks.h"
 
 /*
 BSD 3-Clause License
@@ -53,34 +54,10 @@ Available arguments:
         return 0;
 }*/
 
-static bool startsWithChar(const char *pre, const char str) {
-  char *e;
-  int index;
-  e = strchr(pre, str);
-  index = (int)(e - pre);
-  return index == 0;
-}
-
 static int cmp(const void *a, const void *b) {
   return strcmp(*(char **)a, *(char **)b);
 }
 
-static bool startsWithStr(char *prefix, char *string) {
-  if (strlen(prefix) > strlen(string)) {
-    return false;
-  }
-  int max = strlen(prefix);
-  int i = 0;
-  do {
-    if (prefix[i] == string[i]) {
-      i++;
-    } else {
-      return false;
-    }
-  } while (i < max);
-  return true;
-}
-
 // lots o' code ~~stolen~~ borrowed from
 // https://pubs.opengroup.org/onlinepubs/9699919799/functions/readdir.html
 int main(int argc, char **argv) {