C: binary search

c/binary-search/src/binary_search.c

@@ -0,0 +1,39 @@
+#include "binary_search.h"
+
+const int *binary_search(int v, const int *a, size_t size)
+{
+    size_t lo, hi, i;
+
+    /* quickly exclude invalid/trivial results :
+     * NULL or empty array, value out of bounds
+     */
+    if (!size || !a || v < *a || v > *(a+size-1))
+        return NULL;
+    for (lo=0, hi=size-1, i=hi/2; lo<hi && a[i]!=v; i=lo+(hi-lo)/2) {
+        if (a[i] < v)
+            lo=i+1;
+        else
+            hi=i-1;
+    }
+    return a[i]==v? a+i: NULL;
+}
+
+/* See GNUmakefile below for explanation
+ * https://github.com/braoult/exercism/blob/master/c/templates/GNUmakefile
+ */
+#ifdef UNIT_TEST
+#include <stdio.h>
+int main(int ac, char **av)
+{
+    int arg=1, *res;
+    int i, array[] = {1, 2, 3, 4, 6, 7, 8, 9 };
+    size_t size = sizeof(array) / sizeof(array[0]);
+
+    for (; arg<ac; ++arg) {
+        i=atoi(av[arg]);
+        res=binary_search(i, array, size);
+        printf("binary_search(%d)=%ld\n", i,
+               res? res-array: -1);
+    }
+}
+#endif