mirror of
https://github.com/ziglang/zig.git
synced 2025-12-10 08:13:07 +00:00
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
35 lines
979 B
Zig
35 lines
979 B
Zig
const popcount = @import("popcount.zig");
|
|
const testing = @import("std").testing;
|
|
|
|
fn popcountsi2Naive(a: i32) i32 {
|
|
var x = a;
|
|
var r: i32 = 0;
|
|
while (x != 0) : (x = @bitCast(i32, @bitCast(u32, x) >> 1)) {
|
|
r += @intCast(i32, x & 1);
|
|
}
|
|
return r;
|
|
}
|
|
|
|
fn test__popcountsi2(a: i32) !void {
|
|
const x = popcount.__popcountsi2(a);
|
|
const expected = popcountsi2Naive(a);
|
|
try testing.expectEqual(expected, x);
|
|
}
|
|
|
|
test "popcountsi2" {
|
|
try test__popcountsi2(0);
|
|
try test__popcountsi2(1);
|
|
try test__popcountsi2(2);
|
|
try test__popcountsi2(@bitCast(i32, @as(u32, 0xfffffffd)));
|
|
try test__popcountsi2(@bitCast(i32, @as(u32, 0xfffffffe)));
|
|
try test__popcountsi2(@bitCast(i32, @as(u32, 0xffffffff)));
|
|
|
|
const RndGen = @import("std").rand.DefaultPrng;
|
|
var rnd = RndGen.init(42);
|
|
var i: u32 = 0;
|
|
while (i < 10_000) : (i += 1) {
|
|
var rand_num = rnd.random().int(i32);
|
|
try test__popcountsi2(rand_num);
|
|
}
|
|
}
|