compiler_rt: Move mem implementations from c.zig

This moves functions that LLVM generates calls to,
to the compiler_rt implementation itself, rather than c.zig.
This is a prerequisite for native backends to link with compiler-rt.
This also allows native backends to generate calls to `memcpy` and the like.

1 files changed, 31 insertions, 0 deletions

diff --git a/lib/compiler_rt/memcmp.zig b/lib/compiler_rt/memcmp.zig
new file mode 100644
index 0000000000..b0a925438f
--- /dev/null
+++ b/lib/compiler_rt/memcmp.zig
@@ -0,0 +1,31 @@
+const std = @import("std");
+const common = @import("./common.zig");
+
+comptime {
+    @export(memcmp, .{ .name = "memcmp", .linkage = common.linkage });
+}
+
+pub fn memcmp(vl: ?[*]const u8, vr: ?[*]const u8, n: usize) callconv(.C) c_int {
+    @setRuntimeSafety(false);
+
+    var index: usize = 0;
+    while (index != n) : (index += 1) {
+        const compare_val = @bitCast(i8, vl.?[index] -% vr.?[index]);
+        if (compare_val != 0) {
+            return compare_val;
+        }
+    }
+
+    return 0;
+}
+
+test "memcmp" {
+    const base_arr = &[_]u8{ 1, 1, 1 };
+    const arr1 = &[_]u8{ 1, 1, 1 };
+    const arr2 = &[_]u8{ 1, 0, 1 };
+    const arr3 = &[_]u8{ 1, 2, 1 };
+
+    try std.testing.expect(memcmp(base_arr[0..], arr1[0..], base_arr.len) == 0);
+    try std.testing.expect(memcmp(base_arr[0..], arr2[0..], base_arr.len) > 0);
+    try std.testing.expect(memcmp(base_arr[0..], arr3[0..], base_arr.len) < 0);
+}