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1ea650bb75
- apply simpler approach than LLVM for __popcountdi2
taken from The Art of Computer Programming and generalized
- rename popcountdi2.zig to popcount.zig
- test cases derived from popcountdi2_test.zig
- tests: compare naive approach 10_000 times with
random numbers created from naive seed 42
See #1290
34 lines
1 KiB
Zig
34 lines
1 KiB
Zig
const popcount = @import("popcount.zig");
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const testing = @import("std").testing;
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fn popcountti2Naive(a: i128) i32 {
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var x = a;
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var r: i32 = 0;
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while (x != 0) : (x = @bitCast(i128, @bitCast(u128, x) >> 1)) {
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r += @intCast(i32, x & 1);
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}
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return r;
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}
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fn test__popcountti2(a: i128) !void {
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const x = popcount.__popcountti2(a);
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const expected = popcountti2Naive(a);
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try testing.expectEqual(expected, x);
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}
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test "popcountti2" {
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try test__popcountti2(0);
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try test__popcountti2(1);
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try test__popcountti2(2);
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try test__popcountti2(@bitCast(i128, @as(u128, 0xffffffff_ffffffff_ffffffff_fffffffd)));
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try test__popcountti2(@bitCast(i128, @as(u128, 0xffffffff_ffffffff_ffffffff_fffffffe)));
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try test__popcountti2(@bitCast(i128, @as(u128, 0xffffffff_ffffffff_ffffffff_ffffffff)));
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const RndGen = @import("std").rand.DefaultPrng;
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var rnd = RndGen.init(42);
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var i: u32 = 0;
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while (i < 10_000) : (i += 1) {
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var rand_num = rnd.random().int(i128);
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try test__popcountti2(rand_num);
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}
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}
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