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mirror_qemu/util/bufferiszero.c

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/*
* Simple C functions to supplement the C library
*
* Copyright (c) 2006 Fabrice Bellard
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
#include "qemu/osdep.h"
#include "qemu/cutils.h"
#include "qemu/bswap.h"
#include "host/cpuinfo.h"
typedef bool (*biz_accel_fn)(const void *, size_t);
static bool buffer_is_zero_int_lt256(const void *buf, size_t len)
{
uint64_t t;
const uint64_t *p, *e;
/*
* Use unaligned memory access functions to handle
* the beginning and end of the buffer.
*/
if (unlikely(len <= 8)) {
return (ldl_he_p(buf) | ldl_he_p(buf + len - 4)) == 0;
}
t = ldq_he_p(buf) | ldq_he_p(buf + len - 8);
p = QEMU_ALIGN_PTR_DOWN(buf + 8, 8);
e = QEMU_ALIGN_PTR_DOWN(buf + len - 1, 8);
/* Read 0 to 31 aligned words from the middle. */
while (p < e) {
t |= *p++;
}
return t == 0;
}
static bool buffer_is_zero_int_ge256(const void *buf, size_t len)
{
/*
* Use unaligned memory access functions to handle
* the beginning and end of the buffer.
*/
uint64_t t = ldq_he_p(buf) | ldq_he_p(buf + len - 8);
const uint64_t *p = QEMU_ALIGN_PTR_DOWN(buf + 8, 8);
const uint64_t *e = QEMU_ALIGN_PTR_DOWN(buf + len - 1, 8);
/* Collect a partial block at the tail end. */
t |= e[-7] | e[-6] | e[-5] | e[-4] | e[-3] | e[-2] | e[-1];
/*
* Loop over 64 byte blocks.
* With the head and tail removed, e - p >= 30,
* so the loop must iterate at least 3 times.
*/
do {
if (t) {
return false;
}
t = p[0] | p[1] | p[2] | p[3] | p[4] | p[5] | p[6] | p[7];
p += 8;
} while (p < e - 7);
return t == 0;
}
#if defined(CONFIG_AVX2_OPT) || defined(__SSE2__)
#include <immintrin.h>
/* Helper for preventing the compiler from reassociating
chains of binary vector operations. */
#define SSE_REASSOC_BARRIER(vec0, vec1) asm("" : "+x"(vec0), "+x"(vec1))
/* Note that these vectorized functions may assume len >= 256. */
static bool __attribute__((target("sse2")))
buffer_zero_sse2(const void *buf, size_t len)
{
/* Unaligned loads at head/tail. */
__m128i v = *(__m128i_u *)(buf);
__m128i w = *(__m128i_u *)(buf + len - 16);
/* Align head/tail to 16-byte boundaries. */
const __m128i *p = QEMU_ALIGN_PTR_DOWN(buf + 16, 16);
const __m128i *e = QEMU_ALIGN_PTR_DOWN(buf + len - 1, 16);
__m128i zero = { 0 };
/* Collect a partial block at tail end. */
v |= e[-1]; w |= e[-2];
SSE_REASSOC_BARRIER(v, w);
v |= e[-3]; w |= e[-4];
SSE_REASSOC_BARRIER(v, w);
v |= e[-5]; w |= e[-6];
SSE_REASSOC_BARRIER(v, w);
v |= e[-7]; v |= w;
/*
* Loop over complete 128-byte blocks.
* With the head and tail removed, e - p >= 14, so the loop
* must iterate at least once.
*/
do {
v = _mm_cmpeq_epi8(v, zero);
if (unlikely(_mm_movemask_epi8(v) != 0xFFFF)) {
return false;
}
v = p[0]; w = p[1];
SSE_REASSOC_BARRIER(v, w);
v |= p[2]; w |= p[3];
SSE_REASSOC_BARRIER(v, w);
v |= p[4]; w |= p[5];
SSE_REASSOC_BARRIER(v, w);
v |= p[6]; w |= p[7];
SSE_REASSOC_BARRIER(v, w);
v |= w;
p += 8;
} while (p < e - 7);
return _mm_movemask_epi8(_mm_cmpeq_epi8(v, zero)) == 0xFFFF;
}
#ifdef CONFIG_AVX2_OPT
static bool __attribute__((target("avx2")))
buffer_zero_avx2(const void *buf, size_t len)
{
/* Unaligned loads at head/tail. */
__m256i v = *(__m256i_u *)(buf);
__m256i w = *(__m256i_u *)(buf + len - 32);
/* Align head/tail to 32-byte boundaries. */
const __m256i *p = QEMU_ALIGN_PTR_DOWN(buf + 32, 32);
const __m256i *e = QEMU_ALIGN_PTR_DOWN(buf + len - 1, 32);
__m256i zero = { 0 };
/* Collect a partial block at tail end. */
v |= e[-1]; w |= e[-2];
SSE_REASSOC_BARRIER(v, w);
v |= e[-3]; w |= e[-4];
SSE_REASSOC_BARRIER(v, w);
v |= e[-5]; w |= e[-6];
SSE_REASSOC_BARRIER(v, w);
v |= e[-7]; v |= w;
/* Loop over complete 256-byte blocks. */
for (; p < e - 7; p += 8) {
/* PTEST is not profitable here. */
v = _mm256_cmpeq_epi8(v, zero);
if (unlikely(_mm256_movemask_epi8(v) != 0xFFFFFFFF)) {
return false;
}
v = p[0]; w = p[1];
SSE_REASSOC_BARRIER(v, w);
v |= p[2]; w |= p[3];
SSE_REASSOC_BARRIER(v, w);
v |= p[4]; w |= p[5];
SSE_REASSOC_BARRIER(v, w);
v |= p[6]; w |= p[7];
SSE_REASSOC_BARRIER(v, w);
v |= w;
}
return _mm256_movemask_epi8(_mm256_cmpeq_epi8(v, zero)) == 0xFFFFFFFF;
}
#endif /* CONFIG_AVX2_OPT */
static biz_accel_fn const accel_table[] = {
buffer_is_zero_int_ge256,
buffer_zero_sse2,
#ifdef CONFIG_AVX2_OPT
buffer_zero_avx2,
#endif
};
static unsigned best_accel(void)
{
unsigned info = cpuinfo_init();
#ifdef CONFIG_AVX2_OPT
if (info & CPUINFO_AVX2) {
return 2;
}
#endif
return info & CPUINFO_SSE2 ? 1 : 0;
}
#elif defined(__aarch64__) && defined(__ARM_NEON)
#include <arm_neon.h>
/*
* Helper for preventing the compiler from reassociating
* chains of binary vector operations.
*/
#define REASSOC_BARRIER(vec0, vec1) asm("" : "+w"(vec0), "+w"(vec1))
static bool buffer_is_zero_simd(const void *buf, size_t len)
{
uint32x4_t t0, t1, t2, t3;
/* Align head/tail to 16-byte boundaries. */
const uint32x4_t *p = QEMU_ALIGN_PTR_DOWN(buf + 16, 16);
const uint32x4_t *e = QEMU_ALIGN_PTR_DOWN(buf + len - 1, 16);
/* Unaligned loads at head/tail. */
t0 = vld1q_u32(buf) | vld1q_u32(buf + len - 16);
/* Collect a partial block at tail end. */
t1 = e[-7] | e[-6];
t2 = e[-5] | e[-4];
t3 = e[-3] | e[-2];
t0 |= e[-1];
REASSOC_BARRIER(t0, t1);
REASSOC_BARRIER(t2, t3);
t0 |= t1;
t2 |= t3;
REASSOC_BARRIER(t0, t2);
t0 |= t2;
/*
* Loop over complete 128-byte blocks.
* With the head and tail removed, e - p >= 14, so the loop
* must iterate at least once.
*/
do {
/*
* Reduce via UMAXV. Whatever the actual result,
* it will only be zero if all input bytes are zero.
*/
if (unlikely(vmaxvq_u32(t0) != 0)) {
return false;
}
t0 = p[0] | p[1];
t1 = p[2] | p[3];
t2 = p[4] | p[5];
t3 = p[6] | p[7];
REASSOC_BARRIER(t0, t1);
REASSOC_BARRIER(t2, t3);
t0 |= t1;
t2 |= t3;
REASSOC_BARRIER(t0, t2);
t0 |= t2;
p += 8;
} while (p < e - 7);
return vmaxvq_u32(t0) == 0;
}
#define best_accel() 1
static biz_accel_fn const accel_table[] = {
buffer_is_zero_int_ge256,
buffer_is_zero_simd,
};
#else
#define best_accel() 0
static biz_accel_fn const accel_table[1] = {
buffer_is_zero_int_ge256
};
#endif
static biz_accel_fn buffer_is_zero_accel;
static unsigned accel_index;
bool buffer_is_zero_ool(const void *buf, size_t len)
{
if (unlikely(len == 0)) {
return true;
}
if (!buffer_is_zero_sample3(buf, len)) {
return false;
}
/* All bytes are covered for any len <= 3. */
if (unlikely(len <= 3)) {
return true;
}
if (likely(len >= 256)) {
return buffer_is_zero_accel(buf, len);
}
return buffer_is_zero_int_lt256(buf, len);
}
bool buffer_is_zero_ge256(const void *buf, size_t len)
{
return buffer_is_zero_accel(buf, len);
}
bool test_buffer_is_zero_next_accel(void)
{
if (accel_index != 0) {
buffer_is_zero_accel = accel_table[--accel_index];
return true;
}
return false;
}
static void __attribute__((constructor)) init_accel(void)
{
accel_index = best_accel();
buffer_is_zero_accel = accel_table[accel_index];
}
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