add the std::sort::binarysearch module

Signed-off-by: Pierre Curto <pierre.curto@gmail.com>

lib/std/sort/binarysearch.c3

@@ -0,0 +1,66 @@
+module std::sort::binarysearch;
+
+/*
+ * Compare x and y and return one of the following values:
+ *  -1 if x < y
+ *  0 if x == y
+ *  1 if x > y
+ */
+def Comparer = fn int (void *x, void *y);
+
+/**
+ * Perform a binary search over the sorted array and return the smallest index
+ * in [0, array.len) where cmp(i) is true and cmp(j) is true for j in [i, array.len).
+ * @require is_array_or_subarray(array) "array must be an array or subarray"
+ **/
+macro usz cmp_search(array, x, Comparer cmp)
+{
+    usz i;
+    for (usz j = array.len; i < j;)
+    {
+        usz half = (i + j) / 2;
+        int res = cmp(&array[half], &x);
+        switch {
+            case res > 0: j = half;
+            case res < 0: i = half + 1;
+            default: return half;
+        }
+    }
+    return i;
+}
+
+/**
+ * Perform a binary search over the sorted array and return the index
+ * in [0, array.len) where x would be inserted.
+ * @require is_array_or_subarray(array) "array must be an array or subarray"
+ **/
+macro usz search(array, x)
+{
+    usz i;
+    for (usz j = array.len; i < j;)
+    {
+        usz half = (i + j) / 2;
+        switch {
+            case greater(array[half], x): j = half;
+            case less(array[half], x): i = half + 1;
+            default: return half;
+        }
+    }
+    return i;
+}
+
+macro bool is_array_or_subarray(slice) @private
+{
+    $switch ($typeof(slice).kindof)
+    $case POINTER:
+        var $Inner = $typefrom($typeof(bytes).inner);
+        $if $Inner.kindof == ARRAY:
+            return true;
+        $endif
+    $case ARRAY:
+    $case SUBARRAY:
+        return true;
+    $default:
+	    return false;
+    $endswitch
+}

test/unit/stdlib/sort/binarysearch.c3

@@ -0,0 +1,37 @@
+module binarysearch_test @test;
+import std::sort::binarysearch;
+
+struct SearchTest
+{
+    int[] data;
+    int x;
+    int index;
+}
+
+fn void search()
+{
+    SearchTest[] tcases = {
+        { {}, 0, 0 },
+        { {1, 2, 3}, 1, 0 },
+        { {1, 2, 3}, 2, 1 },
+        { {1, 2, 3}, 3, 2 },
+        { {1, 2, 3}, 4, 3 },
+        { {10, 20, 30}, 14, 1 },
+        { {10, 20, 30}, 26, 2 },
+    };
+
+    foreach (tc : tcases)
+    {
+        usz idx = binarysearch::search(tc.data, tc.x);
+        assert(idx == tc.index, "%s: got %d; want %d", tc.data, idx, tc.index);
+
+        usz cmp_idx = binarysearch::cmp_search(tc.data, tc.x, &cmp_int);
+        assert(cmp_idx == tc.index, "%s: got %d; want %d", tc.data, cmp_idx, tc.index);
+    }
+}
+
+module binarysearch_test;
+
+fn int cmp_int(void* x, void* y) {
+    return *(int*)x - *(int*)y;
+}