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e4c053f047
- use Bit Twiddling Hacks: Compute parity in parallel - test cases derived from popcount.zig - tests: compare naive approach 10_000 times with random numbers created from naive seed 42 - compiler_rt.zig: sort by LLVM builtin order and add comments to improve structure See #1290
41 lines
1.2 KiB
Zig
41 lines
1.2 KiB
Zig
const std = @import("std");
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const builtin = @import("builtin");
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// parity - if number of bits set is even => 0, else => 1
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// - pariytXi2_generic for big and little endian
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fn parityXi2_generic(comptime T: type) fn (a: T) callconv(.C) i32 {
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return struct {
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fn f(a: T) callconv(.C) i32 {
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@setRuntimeSafety(builtin.is_test);
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var x = switch (@bitSizeOf(T)) {
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32 => @bitCast(u32, a),
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64 => @bitCast(u64, a),
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128 => @bitCast(u128, a),
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else => unreachable,
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};
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// Bit Twiddling Hacks: Compute parity in parallel
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comptime var shift: u8 = @bitSizeOf(T) / 2;
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inline while (shift > 2) {
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x ^= x >> shift;
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shift = shift >> 1;
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}
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x &= 0xf;
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return (@intCast(u16, 0x6996) >> @intCast(u4, x)) & 1; // optimization for >>2 and >>1
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}
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}.f;
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}
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pub const __paritysi2 = parityXi2_generic(i32);
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pub const __paritydi2 = parityXi2_generic(i64);
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pub const __parityti2 = parityXi2_generic(i128);
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test {
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_ = @import("paritysi2_test.zig");
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_ = @import("paritydi2_test.zig");
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_ = @import("parityti2_test.zig");
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}
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