tiny.simd.cast

1const std = @import("std");23pub fn bitCast(comptime D: type, value: anytype) D.Vector {4    if (@bitSizeOf(@TypeOf(value)) / 8 != D.byte_count) {5        @compileError("bitCast requires equal source and destination byte sizes");6    }7    return @bitCast(value);8}910pub fn resizeBitCast(comptime D: type, value: anytype) D.Vector {11    return resize(D, value);12}1314pub fn zeroExtendResizeBitCast(15    comptime DTo: type,16    comptime DFrom: type,17    value: DFrom.Vector,18) DTo.Vector {19    return resize(DTo, value);20}2122fn resize(comptime D: type, value: anytype) D.Vector {23    const source_byte_count = @bitSizeOf(@TypeOf(value)) / 8;24    const SourceBytes = [source_byte_count]u8;25    const source: SourceBytes = @bitCast(value);26    var target: [D.byte_count]u8 = @splat(0);27    inline for (0..@min(source_byte_count, D.byte_count)) |index| {28        target[index] = source[index];29    }30    return @bitCast(target);31}3233test "Highway bit casts preserve every source bit" {34    const simd = @import("root.zig");35    const DW = simd.FixedTag(u32, 4);36    const DB = simd.FixedTag(u8, 16);37    const words: DW.Vector = .{ 0x0123_4567, 0x89ab_cdef, 0, 0xffff_ffff };38    const bytes = bitCast(DB, words);39    try std.testing.expect(@reduce(.And, bitCast(DW, bytes) == words));40}4142test "Highway resize casts retain low-address bytes and zero extensions" {43    const simd = @import("root.zig");44    const D = simd.FixedTag(u16, 8);45    const DH = simd.FixedTag(u16, 4);46    const DT = simd.FixedTag(u16, 16);47    const value: D.Vector = .{ 1, 2, 3, 4, 5, 6, 7, 8 };48    try std.testing.expect(@reduce(.And, resizeBitCast(DH, value) ==49        @as(DH.Vector, .{ 1, 2, 3, 4 })));50    try std.testing.expect(@reduce(.And, zeroExtendResizeBitCast(DT, D, value) ==51        @as(DT.Vector, .{ 1, 2, 3, 4, 5, 6, 7, 8, 0, 0, 0, 0, 0, 0, 0, 0 })));52}5354test "Highway resize casts work across lane types" {55    const simd = @import("root.zig");56    inline for (.{ u8, i8, u16, i16, u32, i32, u64, i64, f16, f32, f64 }) |T| {57        const D = simd.FixedTag(T, 4);58        const DB = simd.FixedTag(u8, D.byte_count);59        const DT = simd.FixedTag(T, 8);60        const value: D.Vector = @splat(0);61        try std.testing.expect(@reduce(.And, bitCast(D, bitCast(DB, value)) == value));62        const extended = zeroExtendResizeBitCast(DT, D, value);63        try std.testing.expect(@reduce(.And, resizeBitCast(D, extended) == value));64        try std.testing.expect(@reduce(.And, extended == @as(DT.Vector, @splat(0))));65    }66}

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