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Use memcpy-based peeks and pokes on Microsoft C
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I don't have a Windows machine readily available, but according to
https://godbolt.org/z/q4MfjzTPh and the https://imgur.com/UD5a7MF
profile mentioned in #72, this could improve inner loop performance.

Updates #72
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@nigeltao
nigeltao committed Jun 12, 2022
1 parent 45a7992 commit c226ed6
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Showing 2 changed files with 116 additions and 6 deletions.
61 changes: 58 additions & 3 deletions internal/cgen/base/fundamental-public.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -797,6 +797,22 @@ wuffs_base__count_leading_zeroes_u64(uint64_t u) {

// --------

// Normally, the wuffs_base__peek_etc and wuffs_base__poke_etc implementations
// are both (1) correct regardless of CPU endianness and (2) very fast (e.g. an
// inlined wuffs_base__peek_u32le__no_bounds_check call, in an optimized clang
// or gcc build, is a single MOV instruction on x86_64).
//
// However, the endian-agnostic implementations are slow on Microsoft's C
// compiler (MSC). Alternative memcpy-based implementations restore speed, but
// they are only correct on little-endian CPU architectures. Defining
// WUFFS_BASE__USE_MEMCPY_LE_PEEK_POKE opts in to these implementations.
//
// https://godbolt.org/z/q4MfjzTPh
#if defined(_MSC_VER) && !defined(__clang__) && \
(defined(_M_ARM64) || defined(_M_X64))
#define WUFFS_BASE__USE_MEMCPY_LE_PEEK_POKE
#endif

#define wuffs_base__peek_u8be__no_bounds_check \
wuffs_base__peek_u8__no_bounds_check
#define wuffs_base__peek_u8le__no_bounds_check \
Expand All @@ -809,12 +825,24 @@ wuffs_base__peek_u8__no_bounds_check(const uint8_t* p) {

static inline uint16_t //
wuffs_base__peek_u16be__no_bounds_check(const uint8_t* p) {
#if defined(WUFFS_BASE__USE_MEMCPY_LE_PEEK_POKE)
uint16_t x;
memcpy(&x, p, 2);
return _byteswap_ushort(x);
#else
return (uint16_t)(((uint16_t)(p[0]) << 8) | ((uint16_t)(p[1]) << 0));
#endif
}

static inline uint16_t //
wuffs_base__peek_u16le__no_bounds_check(const uint8_t* p) {
#if defined(WUFFS_BASE__USE_MEMCPY_LE_PEEK_POKE)
uint16_t x;
memcpy(&x, p, 2);
return x;
#else
return (uint16_t)(((uint16_t)(p[0]) << 0) | ((uint16_t)(p[1]) << 8));
#endif
}

static inline uint32_t //
Expand All @@ -831,14 +859,26 @@ wuffs_base__peek_u24le__no_bounds_check(const uint8_t* p) {

static inline uint32_t //
wuffs_base__peek_u32be__no_bounds_check(const uint8_t* p) {
#if defined(WUFFS_BASE__USE_MEMCPY_LE_PEEK_POKE)
uint32_t x;
memcpy(&x, p, 4);
return _byteswap_ulong(x);
#else
return ((uint32_t)(p[0]) << 24) | ((uint32_t)(p[1]) << 16) |
((uint32_t)(p[2]) << 8) | ((uint32_t)(p[3]) << 0);
#endif
}

static inline uint32_t //
wuffs_base__peek_u32le__no_bounds_check(const uint8_t* p) {
#if defined(WUFFS_BASE__USE_MEMCPY_LE_PEEK_POKE)
uint32_t x;
memcpy(&x, p, 4);
return x;
#else
return ((uint32_t)(p[0]) << 0) | ((uint32_t)(p[1]) << 8) |
((uint32_t)(p[2]) << 16) | ((uint32_t)(p[3]) << 24);
#endif
}

static inline uint64_t //
Expand Down Expand Up @@ -887,18 +927,30 @@ wuffs_base__peek_u56le__no_bounds_check(const uint8_t* p) {

static inline uint64_t //
wuffs_base__peek_u64be__no_bounds_check(const uint8_t* p) {
#if defined(WUFFS_BASE__USE_MEMCPY_LE_PEEK_POKE)
uint64_t x;
memcpy(&x, p, 8);
return _byteswap_uint64(x);
#else
return ((uint64_t)(p[0]) << 56) | ((uint64_t)(p[1]) << 48) |
((uint64_t)(p[2]) << 40) | ((uint64_t)(p[3]) << 32) |
((uint64_t)(p[4]) << 24) | ((uint64_t)(p[5]) << 16) |
((uint64_t)(p[6]) << 8) | ((uint64_t)(p[7]) << 0);
#endif
}

static inline uint64_t //
wuffs_base__peek_u64le__no_bounds_check(const uint8_t* p) {
#if defined(WUFFS_BASE__USE_MEMCPY_LE_PEEK_POKE)
uint64_t x;
memcpy(&x, p, 8);
return x;
#else
return ((uint64_t)(p[0]) << 0) | ((uint64_t)(p[1]) << 8) |
((uint64_t)(p[2]) << 16) | ((uint64_t)(p[3]) << 24) |
((uint64_t)(p[4]) << 32) | ((uint64_t)(p[5]) << 40) |
((uint64_t)(p[6]) << 48) | ((uint64_t)(p[7]) << 56);
#endif
}

// --------
Expand All @@ -921,7 +973,8 @@ wuffs_base__poke_u16be__no_bounds_check(uint8_t* p, uint16_t x) {

static inline void //
wuffs_base__poke_u16le__no_bounds_check(uint8_t* p, uint16_t x) {
#if defined(__GNUC__) && !defined(__clang__) && defined(__x86_64__)
#if defined(WUFFS_BASE__USE_MEMCPY_LE_PEEK_POKE) || \
(defined(__GNUC__) && !defined(__clang__) && defined(__x86_64__))
// This seems to perform better on gcc 10 (but not clang 9). Clang also
// defines "__GNUC__".
memcpy(p, &x, 2);
Expand Down Expand Up @@ -955,7 +1008,8 @@ wuffs_base__poke_u32be__no_bounds_check(uint8_t* p, uint32_t x) {

static inline void //
wuffs_base__poke_u32le__no_bounds_check(uint8_t* p, uint32_t x) {
#if defined(__GNUC__) && !defined(__clang__) && defined(__x86_64__)
#if defined(WUFFS_BASE__USE_MEMCPY_LE_PEEK_POKE) || \
(defined(__GNUC__) && !defined(__clang__) && defined(__x86_64__))
// This seems to perform better on gcc 10 (but not clang 9). Clang also
// defines "__GNUC__".
memcpy(p, &x, 4);
Expand Down Expand Up @@ -1041,7 +1095,8 @@ wuffs_base__poke_u64be__no_bounds_check(uint8_t* p, uint64_t x) {

static inline void //
wuffs_base__poke_u64le__no_bounds_check(uint8_t* p, uint64_t x) {
#if defined(__GNUC__) && !defined(__clang__) && defined(__x86_64__)
#if defined(WUFFS_BASE__USE_MEMCPY_LE_PEEK_POKE) || \
(defined(__GNUC__) && !defined(__clang__) && defined(__x86_64__))
// This seems to perform better on gcc 10 (but not clang 9). Clang also
// defines "__GNUC__".
memcpy(p, &x, 8);
Expand Down
61 changes: 58 additions & 3 deletions release/c/wuffs-unsupported-snapshot.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1064,6 +1064,22 @@ wuffs_base__count_leading_zeroes_u64(uint64_t u) {

// --------

// Normally, the wuffs_base__peek_etc and wuffs_base__poke_etc implementations
// are both (1) correct regardless of CPU endianness and (2) very fast (e.g. an
// inlined wuffs_base__peek_u32le__no_bounds_check call, in an optimized clang
// or gcc build, is a single MOV instruction on x86_64).
//
// However, the endian-agnostic implementations are slow on Microsoft's C
// compiler (MSC). Alternative memcpy-based implementations restore speed, but
// they are only correct on little-endian CPU architectures. Defining
// WUFFS_BASE__USE_MEMCPY_LE_PEEK_POKE opts in to these implementations.
//
// https://godbolt.org/z/q4MfjzTPh
#if defined(_MSC_VER) && !defined(__clang__) && \
(defined(_M_ARM64) || defined(_M_X64))
#define WUFFS_BASE__USE_MEMCPY_LE_PEEK_POKE
#endif

#define wuffs_base__peek_u8be__no_bounds_check \
wuffs_base__peek_u8__no_bounds_check
#define wuffs_base__peek_u8le__no_bounds_check \
Expand All @@ -1076,12 +1092,24 @@ wuffs_base__peek_u8__no_bounds_check(const uint8_t* p) {

static inline uint16_t //
wuffs_base__peek_u16be__no_bounds_check(const uint8_t* p) {
#if defined(WUFFS_BASE__USE_MEMCPY_LE_PEEK_POKE)
uint16_t x;
memcpy(&x, p, 2);
return _byteswap_ushort(x);
#else
return (uint16_t)(((uint16_t)(p[0]) << 8) | ((uint16_t)(p[1]) << 0));
#endif
}

static inline uint16_t //
wuffs_base__peek_u16le__no_bounds_check(const uint8_t* p) {
#if defined(WUFFS_BASE__USE_MEMCPY_LE_PEEK_POKE)
uint16_t x;
memcpy(&x, p, 2);
return x;
#else
return (uint16_t)(((uint16_t)(p[0]) << 0) | ((uint16_t)(p[1]) << 8));
#endif
}

static inline uint32_t //
Expand All @@ -1098,14 +1126,26 @@ wuffs_base__peek_u24le__no_bounds_check(const uint8_t* p) {

static inline uint32_t //
wuffs_base__peek_u32be__no_bounds_check(const uint8_t* p) {
#if defined(WUFFS_BASE__USE_MEMCPY_LE_PEEK_POKE)
uint32_t x;
memcpy(&x, p, 4);
return _byteswap_ulong(x);
#else
return ((uint32_t)(p[0]) << 24) | ((uint32_t)(p[1]) << 16) |
((uint32_t)(p[2]) << 8) | ((uint32_t)(p[3]) << 0);
#endif
}

static inline uint32_t //
wuffs_base__peek_u32le__no_bounds_check(const uint8_t* p) {
#if defined(WUFFS_BASE__USE_MEMCPY_LE_PEEK_POKE)
uint32_t x;
memcpy(&x, p, 4);
return x;
#else
return ((uint32_t)(p[0]) << 0) | ((uint32_t)(p[1]) << 8) |
((uint32_t)(p[2]) << 16) | ((uint32_t)(p[3]) << 24);
#endif
}

static inline uint64_t //
Expand Down Expand Up @@ -1154,18 +1194,30 @@ wuffs_base__peek_u56le__no_bounds_check(const uint8_t* p) {

static inline uint64_t //
wuffs_base__peek_u64be__no_bounds_check(const uint8_t* p) {
#if defined(WUFFS_BASE__USE_MEMCPY_LE_PEEK_POKE)
uint64_t x;
memcpy(&x, p, 8);
return _byteswap_uint64(x);
#else
return ((uint64_t)(p[0]) << 56) | ((uint64_t)(p[1]) << 48) |
((uint64_t)(p[2]) << 40) | ((uint64_t)(p[3]) << 32) |
((uint64_t)(p[4]) << 24) | ((uint64_t)(p[5]) << 16) |
((uint64_t)(p[6]) << 8) | ((uint64_t)(p[7]) << 0);
#endif
}

static inline uint64_t //
wuffs_base__peek_u64le__no_bounds_check(const uint8_t* p) {
#if defined(WUFFS_BASE__USE_MEMCPY_LE_PEEK_POKE)
uint64_t x;
memcpy(&x, p, 8);
return x;
#else
return ((uint64_t)(p[0]) << 0) | ((uint64_t)(p[1]) << 8) |
((uint64_t)(p[2]) << 16) | ((uint64_t)(p[3]) << 24) |
((uint64_t)(p[4]) << 32) | ((uint64_t)(p[5]) << 40) |
((uint64_t)(p[6]) << 48) | ((uint64_t)(p[7]) << 56);
#endif
}

// --------
Expand All @@ -1188,7 +1240,8 @@ wuffs_base__poke_u16be__no_bounds_check(uint8_t* p, uint16_t x) {

static inline void //
wuffs_base__poke_u16le__no_bounds_check(uint8_t* p, uint16_t x) {
#if defined(__GNUC__) && !defined(__clang__) && defined(__x86_64__)
#if defined(WUFFS_BASE__USE_MEMCPY_LE_PEEK_POKE) || \
(defined(__GNUC__) && !defined(__clang__) && defined(__x86_64__))
// This seems to perform better on gcc 10 (but not clang 9). Clang also
// defines "__GNUC__".
memcpy(p, &x, 2);
Expand Down Expand Up @@ -1222,7 +1275,8 @@ wuffs_base__poke_u32be__no_bounds_check(uint8_t* p, uint32_t x) {

static inline void //
wuffs_base__poke_u32le__no_bounds_check(uint8_t* p, uint32_t x) {
#if defined(__GNUC__) && !defined(__clang__) && defined(__x86_64__)
#if defined(WUFFS_BASE__USE_MEMCPY_LE_PEEK_POKE) || \
(defined(__GNUC__) && !defined(__clang__) && defined(__x86_64__))
// This seems to perform better on gcc 10 (but not clang 9). Clang also
// defines "__GNUC__".
memcpy(p, &x, 4);
Expand Down Expand Up @@ -1308,7 +1362,8 @@ wuffs_base__poke_u64be__no_bounds_check(uint8_t* p, uint64_t x) {

static inline void //
wuffs_base__poke_u64le__no_bounds_check(uint8_t* p, uint64_t x) {
#if defined(__GNUC__) && !defined(__clang__) && defined(__x86_64__)
#if defined(WUFFS_BASE__USE_MEMCPY_LE_PEEK_POKE) || \
(defined(__GNUC__) && !defined(__clang__) && defined(__x86_64__))
// This seems to perform better on gcc 10 (but not clang 9). Clang also
// defines "__GNUC__".
memcpy(p, &x, 8);
Expand Down

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