25 lines
1.0 KiB
Zig
25 lines
1.0 KiB
Zig
const builtin = @import("builtin");
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const compiler_rt = @import("../compiler_rt.zig");
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// ported from llvm compiler-rt 8.0.0rc3 95e1c294cb0415a377a7b1d6c7c7d4f89e1c04e4
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pub extern fn __popcountdi2(a: i64) i32 {
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var x2 = @bitCast(u64, a);
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x2 = x2 - ((x2 >> 1) & 0x5555555555555555);
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// Every 2 bits holds the sum of every pair of bits (32)
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x2 = ((x2 >> 2) & 0x3333333333333333) + (x2 & 0x3333333333333333);
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// Every 4 bits holds the sum of every 4-set of bits (3 significant bits) (16)
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x2 = (x2 + (x2 >> 4)) & 0x0F0F0F0F0F0F0F0F;
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// Every 8 bits holds the sum of every 8-set of bits (4 significant bits) (8)
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var x: u32 = @truncate(u32, x2 + (x2 >> 32));
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// The lower 32 bits hold four 16 bit sums (5 significant bits).
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// Upper 32 bits are garbage */
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x = x + (x >> 16);
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// The lower 16 bits hold two 32 bit sums (6 significant bits).
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// Upper 16 bits are garbage */
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return @bitCast(i32, (x + (x >> 8)) & 0x0000007F); // (7 significant bits)
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}
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test "import popcountdi2" {
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_ = @import("popcountdi2_test.zig");
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}
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