From 0bf1e9c6112e6fcb6f0e841f135cd5f0e1607483 Mon Sep 17 00:00:00 2001 From: Rekai Musuka Date: Sat, 2 Dec 2023 16:44:29 -0600 Subject: [PATCH] chore: make sw pext generic over T --- src/lib.zig | 72 +++++++++++++++++------------------------------------ 1 file changed, 23 insertions(+), 49 deletions(-) diff --git a/src/lib.zig b/src/lib.zig index f333c16..72747dd 100644 --- a/src/lib.zig +++ b/src/lib.zig @@ -326,62 +326,36 @@ const pext = struct { }; } - fn sw(comptime T: type, value: T, mask: T) T { - // TODO: rewrite in idiomatic zig / understand the algorithm and write an original implementation - // code source: https://stackoverflow.com/questions/41720249/detecting-matching-bits-in-c - // note: will be replaced in the future by https://github.com/ziglang/zig/issues/14995 (hopefully?) + inline fn sw(comptime T: type, value: T, mask: T) T { + // FIXME: will be replaced in the future by https://github.com/ziglang/zig/issues/14995 (hopefully?) return switch (T) { - u32 => { - var _value: T = value; - var _mask: T = mask; + u32, u64 => { + // code source: https://stackoverflow.com/questions/41720249/detecting-matching-bits-in-c + // TODO: rewrite more in generic/idiomatic zig + const log2_bits = @typeInfo(Log2Int(T)).Int.bits; - _value &= _mask; - var mk: T = ~_mask << 1; - var mp: T = undefined; - var mv: T = undefined; - var t: T = undefined; + var val: T = value & mask; + var msk: T = mask; + + var mk: T = ~msk << 1; + + inline for (0..log2_bits) |i| { + var mp: T = mk ^ (mk << 1); + inline for (1..log2_bits) |j| { + mp = mp ^ (mp << (1 << j)); // parallel suffix + } + + const mv = (mp & msk); // bits to move + msk = ((msk ^ mv) | (mv >> (1 << i))); // compress mask + + const t = (val & mv); + val = ((val ^ t) | (t >> (1 << i))); // compress val - inline for (0..@typeInfo(Log2Int(T)).Int.bits) |i| { - mp = mk ^ (mk << 1); // parallel suffix - mp = mp ^ (mp << 2); - mp = mp ^ (mp << 4); - mp = mp ^ (mp << 8); - mp = mp ^ (mp << 16); - mv = (mp & _mask); // bits to move - _mask = ((_mask ^ mv) | (mv >> (1 << i))); // compress _mask - t = (_value & mv); - _value = ((_value ^ t) | (t >> (1 << i))); // compress _value mk &= ~mp; } - return _value; - }, - u64 => { - var _value: T = value; - var _mask: T = mask; - - _value &= _mask; - var mk: T = ~_mask << 1; - var mp: T = undefined; - var mv: T = undefined; - var t: T = undefined; - - inline for (0..@typeInfo(Log2Int(T)).Int.bits) |i| { - mp = mk ^ (mk << 1); // parallel suffix - mp = mp ^ (mp << 2); - mp = mp ^ (mp << 4); - mp = mp ^ (mp << 8); - mp = mp ^ (mp << 16); - mp = mp ^ (mp << 32); - mv = (mp & _mask); // bits to move - _mask = ((_mask ^ mv) | (mv >> (1 << i))); // compress _mask - t = (_value & mv); - _value = ((_value ^ t) | (t >> (1 << i))); // compress _value - mk &= ~mp; - } - - return _value; + return val; }, else => @compileError("pext is sunsupported for " ++ @typeName(T) ++ "."), };