1 files changed, 54 insertions, 0 deletions
diff --git a/lib/std/special/compiler_rt/muldi3.zig b/lib/std/special/compiler_rt/muldi3.zig
new file mode 100644
index 0000000000..7700777c16
--- /dev/null
+++ b/lib/std/special/compiler_rt/muldi3.zig
@@ -0,0 +1,54 @@
+const builtin = @import("builtin");
+
+// Ported from
+// https://github.com/llvm/llvm-project/blob/llvmorg-9.0.0/compiler-rt/lib/builtins/muldi3.c
+
+const dwords = extern union {
+    all: i64,
+    s: switch (builtin.endian) {
+        .Little => extern struct {
+            low: u32,
+            high: u32,
+        },
+        .Big => extern struct {
+            high: u32,
+            low: u32,
+        },
+    },
+};
+
+fn __muldsi3(a: u32, b: u32) i64 {
+    @setRuntimeSafety(builtin.is_test);
+
+    const bits_in_word_2 = @sizeOf(i32) * 8 / 2;
+    const lower_mask = (~u32(0)) >> bits_in_word_2;
+
+    var r: dwords = undefined;
+    r.s.low = (a & lower_mask) *% (b & lower_mask);
+    var t: u32 = r.s.low >> bits_in_word_2;
+    r.s.low &= lower_mask;
+    t += (a >> bits_in_word_2) *% (b & lower_mask);
+    r.s.low +%= (t & lower_mask) << bits_in_word_2;
+    r.s.high = t >> bits_in_word_2;
+    t = r.s.low >> bits_in_word_2;
+    r.s.low &= lower_mask;
+    t +%= (b >> bits_in_word_2) *% (a & lower_mask);
+    r.s.low +%= (t & lower_mask) << bits_in_word_2;
+    r.s.high +%= t >> bits_in_word_2;
+    r.s.high +%= (a >> bits_in_word_2) *% (b >> bits_in_word_2);
+    return r.all;
+}
+
+pub extern fn __muldi3(a: i64, b: i64) i64 {
+    @setRuntimeSafety(builtin.is_test);
+
+    const x = dwords{ .all = a };
+    const y = dwords{ .all = b };
+    var r = dwords{ .all = __muldsi3(x.s.low, y.s.low) };
+    r.s.high +%= x.s.high *% y.s.low +% x.s.low *% y.s.high;
+    return r.all;
+}
+
+test "import muldi3" {
+    _ = @import("muldi3_test.zig");
+}