tiny.simd.sign

1pub const sign = @import("sign.zig");

1const std = @import("std");23pub fn signBit(comptime D: type) D.Vector {4    const U = UnsignedLane(D);5    const mask: U = @as(U, 1) << (@bitSizeOf(D.Lane) - 1);6    return @bitCast(@as(UnsignedVector(D), @splat(mask)));7}89pub fn copySign(comptime D: type, magnitude: D.Vector, sign: D.Vector) D.Vector {10    validateFloat(D);11    const mask: UnsignedVector(D) = @bitCast(signBit(D));12    const magnitude_bits: UnsignedVector(D) = @bitCast(magnitude);13    const sign_bits: UnsignedVector(D) = @bitCast(sign);14    return @bitCast((magnitude_bits & ~mask) | (sign_bits & mask));15}1617pub fn copySignToAbs(comptime D: type, absolute: D.Vector, sign: D.Vector) D.Vector {18    validateFloat(D);19    const mask: UnsignedVector(D) = @bitCast(signBit(D));20    const absolute_bits: UnsignedVector(D) = @bitCast(absolute);21    const sign_bits: UnsignedVector(D) = @bitCast(sign);22    return @bitCast(absolute_bits | (sign_bits & mask));23}2425pub fn broadcastSignBit(comptime D: type, value: D.Vector) D.Vector {26    if (@typeInfo(D.Lane) != .int or27        @typeInfo(D.Lane).int.signedness != .signed)28    {29        @compileError("broadcastSignBit requires signed integer lanes");30    }31    const Amount = @Vector(D.lane_count, std.math.Log2Int(UnsignedLane(D)));32    const amount: Amount = @splat(@bitSizeOf(D.Lane) - 1);33    return value >> amount;34}3536fn UnsignedLane(comptime D: type) type {37    return @Int(.unsigned, @bitSizeOf(D.Lane));38}3940fn UnsignedVector(comptime D: type) type {41    return @Vector(D.lane_count, UnsignedLane(D));42}4344fn validateFloat(comptime D: type) void {45    if (@typeInfo(D.Lane) != .float) @compileError("copySign requires floating-point lanes");46}4748fn verifyBroadcast(comptime T: type) !void {49    const simd = @import("root.zig");50    const D = simd.FixedTag(T, 4);51    const value: D.Vector = .{ 0, 1, -1, std.math.minInt(T) };52    try std.testing.expect(@reduce(.And, broadcastSignBit(D, value) ==53        @as(D.Vector, .{ 0, 0, -1, -1 })));54}5556fn verifyCopySign(comptime T: type) !void {57    const simd = @import("root.zig");58    const D = simd.FixedTag(T, 4);59    const U = @Int(.unsigned, @bitSizeOf(T));60    const UV = @Vector(4, U);61    const sign_mask: U = @as(U, 1) << (@bitSizeOf(T) - 1);62    const one_bits: U = @bitCast(@as(T, 1));63    const signs: D.Vector = @bitCast(@as(UV, .{ 0, sign_mask, sign_mask, 0 }));64    const magnitude: D.Vector = @splat(1);65    const expected: UV = .{ one_bits, one_bits | sign_mask, one_bits | sign_mask, one_bits };66    try std.testing.expect(@reduce(.And, @as(UV, @bitCast(copySign(D, magnitude, signs))) == expected));67    try std.testing.expect(@reduce(.And, @as(UV, @bitCast(copySignToAbs(D, magnitude, signs))) == expected));68}6970test "Highway sign masks copy floating sign bits including negative zero" {71    const simd = @import("root.zig");72    const D = simd.FixedTag(f32, 4);73    const U = simd.FixedTag(u32, 4);74    const magnitude: D.Vector = @bitCast(@as(U.Vector, .{75        0, 0x3f80_0000, 0xc000_0000, 0x7fc0_1234,76    }));77    const sign: D.Vector = @bitCast(@as(U.Vector, .{78        0x8000_0000, 0, 0x8000_0000, 0,79    }));80    const expected: U.Vector = .{81        0x8000_0000, 0x3f80_0000, 0xc000_0000, 0x7fc0_1234,82    };83    try std.testing.expect(@reduce(.And, @as(U.Vector, @bitCast(copySign(D, magnitude, sign))) == expected));84    const absolute: D.Vector = @bitCast(@as(U.Vector, .{85        0, 0x3f80_0000, 0x4000_0000, 0x7fc0_1234,86    }));87    try std.testing.expect(@reduce(.And, @as(U.Vector, @bitCast(copySignToAbs(D, absolute, sign))) == expected));88}8990test "Highway broadcast sign covers all signed lane widths" {91    inline for (.{ i8, i16, i32, i64 }) |T| try verifyBroadcast(T);92}9394test "Highway copy sign covers every floating lane width" {95    inline for (.{ f16, f32, f64 }) |T| try verifyCopySign(T);96}