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/* Basic zero byte detection. Generic C version.
Copyright (C) 2023-2024 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<http://www.gnu.org/licenses/>. */
#ifndef _STRING_FZA_H
#define _STRING_FZA_H 1
#include <string-misc.h>
#include <string-optype.h>
/* The function return a byte mask. */
typedef op_t find_t;
/* This function returns non-zero if any byte in X is zero.
More specifically, at least one bit set within the least significant
byte that was zero; other bytes within the word are indeterminate. */
static __always_inline find_t
find_zero_low (op_t x)
{
/* This expression comes from
https://graphics.stanford.edu/~seander/bithacks.html#ZeroInWord
Subtracting 1 sets 0x80 in a byte that was 0; anding ~x clears
0x80 in a byte that was >= 128; anding 0x80 isolates that test bit. */
op_t lsb = repeat_bytes (0x01);
op_t msb = repeat_bytes (0x80);
return (x - lsb) & ~x & msb;
}
/* This function returns at least one bit set within every byte of X that
is zero. The result is exact in that, unlike find_zero_low, all bytes
are determinate. This is usually used for finding the index of the
most significant byte that was zero. */
static __always_inline find_t
find_zero_all (op_t x)
{
/* For each byte, find not-zero by
(0) And 0x7f so that we cannot carry between bytes,
(1) Add 0x7f so that non-zero carries into 0x80,
(2) Or in the original byte (which might have had 0x80 set).
Then invert and mask such that 0x80 is set iff that byte was zero. */
op_t m = repeat_bytes (0x7f);
return ~(((x & m) + m) | x | m);
}
/* With similar caveats, identify bytes that are equal between X1 and X2. */
static __always_inline find_t
find_eq_low (op_t x1, op_t x2)
{
return find_zero_low (x1 ^ x2);
}
static __always_inline find_t
find_eq_all (op_t x1, op_t x2)
{
return find_zero_all (x1 ^ x2);
}
/* With similar caveats, identify zero bytes in X1 and bytes that are
equal between in X1 and X2. */
static __always_inline find_t
find_zero_eq_low (op_t x1, op_t x2)
{
return find_zero_low (x1) | find_zero_low (x1 ^ x2);
}
static __always_inline find_t
find_zero_eq_all (op_t x1, op_t x2)
{
return find_zero_all (x1) | find_zero_all (x1 ^ x2);
}
/* With similar caveats, identify zero bytes in X1 and bytes that are
not equal between in X1 and X2. */
static __always_inline find_t
find_zero_ne_all (op_t x1, op_t x2)
{
op_t m = repeat_bytes (0x7f);
op_t eq = x1 ^ x2;
op_t nz1 = ((x1 & m) + m) | x1;
op_t ne2 = ((eq & m) + m) | eq;
return (ne2 | ~nz1) & ~m;
}
#endif /* _STRING_FZA_H */
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