std/math.zig: use previous rotate code with non-power-of-two integers

1 files changed, 28 insertions, 4 deletions

diff --git a/lib/std/math.zig b/lib/std/math.zig
index 18c8f555d4..2f16ecb5d8 100644
--- a/lib/std/math.zig
+++ b/lib/std/math.zig
@@ -598,6 +598,8 @@ test "shr" {
 pub fn rotr(comptime T: type, x: T, r: anytype) T {
     if (@typeInfo(T) == .Vector) {
         const C = @typeInfo(T).Vector.child;
+        if (C == u0) return 0;
+
         if (@typeInfo(C).Int.signedness == .signed) {
             @compileError("cannot rotate signed integers");
         }
@@ -606,8 +608,15 @@ pub fn rotr(comptime T: type, x: T, r: anytype) T {
     } else if (@typeInfo(T).Int.signedness == .signed) {
         @compileError("cannot rotate signed integer");
     } else {
-        const ar = @intCast(Log2Int(T), @mod(r, @typeInfo(T).Int.bits));
-        return x >> ar | x << (1 +% ~ar);
+        if (T == u0) return 0;
+
+        if (isPowerOfTwo(@typeInfo(T).Int.bits)) {
+            const ar = @intCast(Log2Int(T), @mod(r, @typeInfo(T).Int.bits));
+            return x >> ar | x << (1 +% ~ar);
+        } else {
+            const ar = @mod(r, @typeInfo(T).Int.bits);
+            return shr(T, x, ar) | shl(T, x, @typeInfo(T).Int.bits - ar);
+        }
     }
 }
 
@@ -618,6 +627,9 @@ test "rotr" {
         // https://github.com/ziglang/zig/issues/12012
         return error.SkipZigTest;
     }
+    try testing.expect(rotr(u0, 0b0, @as(usize, 3)) == 0b0);
+    try testing.expect(rotr(u5, 0b00001, @as(usize, 0)) == 0b00001);
+    try testing.expect(rotr(u6, 0b000001, @as(usize, 7)) == 0b100000);
     try testing.expect(rotr(u8, 0b00000001, @as(usize, 0)) == 0b00000001);
     try testing.expect(rotr(u8, 0b00000001, @as(usize, 9)) == 0b10000000);
     try testing.expect(rotr(u8, 0b00000001, @as(usize, 8)) == 0b00000001);
@@ -632,6 +644,8 @@ test "rotr" {
 pub fn rotl(comptime T: type, x: T, r: anytype) T {
     if (@typeInfo(T) == .Vector) {
         const C = @typeInfo(T).Vector.child;
+        if (C == u0) return 0;
+
         if (@typeInfo(C).Int.signedness == .signed) {
             @compileError("cannot rotate signed integers");
         }
@@ -640,8 +654,15 @@ pub fn rotl(comptime T: type, x: T, r: anytype) T {
     } else if (@typeInfo(T).Int.signedness == .signed) {
         @compileError("cannot rotate signed integer");
     } else {
-        const ar = @intCast(Log2Int(T), @mod(r, @typeInfo(T).Int.bits));
-        return x << ar | x >> 1 +% ~ar;
+        if (T == u0) return 0;
+
+        if (isPowerOfTwo(@typeInfo(T).Int.bits)) {
+            const ar = @intCast(Log2Int(T), @mod(r, @typeInfo(T).Int.bits));
+            return x << ar | x >> 1 +% ~ar;
+        } else {
+            const ar = @mod(r, @typeInfo(T).Int.bits);
+            return shl(T, x, ar) | shr(T, x, @typeInfo(T).Int.bits - ar);
+        }
     }
 }
 
@@ -652,6 +673,9 @@ test "rotl" {
         // https://github.com/ziglang/zig/issues/12012
         return error.SkipZigTest;
     }
+    try testing.expect(rotl(u0, 0b0, @as(usize, 3)) == 0b0);
+    try testing.expect(rotl(u5, 0b00001, @as(usize, 0)) == 0b00001);
+    try testing.expect(rotl(u6, 0b000001, @as(usize, 7)) == 0b000010);
     try testing.expect(rotl(u8, 0b00000001, @as(usize, 0)) == 0b00000001);
     try testing.expect(rotl(u8, 0b00000001, @as(usize, 9)) == 0b00000010);
     try testing.expect(rotl(u8, 0b00000001, @as(usize, 8)) == 0b00000001);