1 files changed, 49 insertions, 0 deletions
diff --git a/lib/std/special/compiler_rt/muloti4.zig b/lib/std/special/compiler_rt/muloti4.zig
new file mode 100644
index 0000000000..ccde8e3e6c
--- /dev/null
+++ b/lib/std/special/compiler_rt/muloti4.zig
@@ -0,0 +1,49 @@
+const builtin = @import("builtin");
+const compiler_rt = @import("../compiler_rt.zig");
+
+pub extern fn __muloti4(a: i128, b: i128, overflow: *c_int) i128 {
+    @setRuntimeSafety(builtin.is_test);
+
+    const min = @bitCast(i128, u128(1 << (i128.bit_count - 1)));
+    const max = ~min;
+    overflow.* = 0;
+
+    const r = a *% b;
+    if (a == min) {
+        if (b != 0 and b != 1) {
+            overflow.* = 1;
+        }
+        return r;
+    }
+    if (b == min) {
+        if (a != 0 and a != 1) {
+            overflow.* = 1;
+        }
+        return r;
+    }
+
+    const sa = a >> (i128.bit_count - 1);
+    const abs_a = (a ^ sa) -% sa;
+    const sb = b >> (i128.bit_count - 1);
+    const abs_b = (b ^ sb) -% sb;
+
+    if (abs_a < 2 or abs_b < 2) {
+        return r;
+    }
+
+    if (sa == sb) {
+        if (abs_a > @divTrunc(max, abs_b)) {
+            overflow.* = 1;
+        }
+    } else {
+        if (abs_a > @divTrunc(min, -abs_b)) {
+            overflow.* = 1;
+        }
+    }
+
+    return r;
+}
+
+test "import muloti4" {
+    _ = @import("muloti4_test.zig");
+}