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fix ffs

This commit is contained in:
lizzie 2025-12-29 08:55:15 +00:00 committed by crueter
parent c394cc704e
commit 212eb4ced3
1 changed files with 16 additions and 3 deletions
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19
externals/bc_decoder/bc_decoder.cpp vendored
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@ -8,10 +8,9 @@
#include <array>
#include <assert.h>
#include <bit>
#include <stddef.h>
#include <stdint.h>
#include <strings.h>
#include <bit>
namespace {
constexpr int32_t BlockWidth = 4;
@ -1040,7 +1039,21 @@ namespace {
/**/ {0x6, 0x1, 0x0, 0x0, 0x0, 0x7, 0x7, 0x1, 0x0, 0x4, 0x3f, 0x0},
/**/ {0x7, 0x2, 0x6, 0x0, 0x0, 0x5, 0x5, 0x1, 0x0, 0x2, 0x1e, 0x0},
};
return m_table[::ffs(low & 0b11111111)];
// Fun historical fact: this is basically ffs(), however, windows does NOT have ffs()
// This is because ffs() comes from VAX which had an instruction for ffs(), but
// to the surprise of absolutely nobody, VAX ended up dying, alongside ffs()... or so
// I tought. It turns out only *NIX world kept ffs() while windows, not bound by POSIX
// standards, just dropped it altogether. Even through Windows had a VAX port at once time
// there isn't much one can do other than scream.
if ((low & 0b00000001) != 0) return m_table[0];
else if ((low & 0b00000010) != 0) return m_table[1];
else if ((low & 0b00000100) != 0) return m_table[2];
else if ((low & 0b00001000) != 0) return m_table[3];
else if ((low & 0b00010000) != 0) return m_table[4];
else if ((low & 0b00100000) != 0) return m_table[5];
else if ((low & 0b01000000) != 0) return m_table[6];
else if ((low & 0b10000000) != 0) return m_table[7];
return m_table[0]; //invalid but pretend it's fine
}
struct IndexInfo {