diff options
Diffstat (limited to '')
| -rw-r--r-- | src/common/tuklib_integer.h | 256 |
1 files changed, 189 insertions, 67 deletions
diff --git a/src/common/tuklib_integer.h b/src/common/tuklib_integer.h index 0eaca369..e22aa8ad 100644 --- a/src/common/tuklib_integer.h +++ b/src/common/tuklib_integer.h @@ -195,6 +195,9 @@ // Unaligned reads and writes // //////////////////////////////// +// No-strict-align archs like x86-64 +// --------------------------------- +// // The traditional way of casting e.g. *(const uint16_t *)uint8_pointer // is bad even if the uint8_pointer is properly aligned because this kind // of casts break strict aliasing rules and result in undefined behavior. @@ -209,12 +212,115 @@ // build time. A third method, casting to a packed struct, would also be // an option but isn't provided to keep things simpler (it's already a mess). // Hopefully this is flexible enough in practice. +// +// Some compilers on x86-64 like Clang >= 10 and GCC >= 5.1 detect that +// +// buf[0] | (buf[1] << 8) +// +// reads a 16-bit value and can emit a single 16-bit load and produce +// identical code than with the memcpy() method. In other cases Clang and GCC +// produce either the same or better code with memcpy(). For example, Clang 9 +// on x86-64 can detect 32-bit load but not 16-bit load. +// +// MSVC uses unaligned access with the memcpy() method but emits byte-by-byte +// code for "buf[0] | (buf[1] << 8)". +// +// Conclusion: The memcpy() method is the best choice when unaligned access +// is supported. +// +// Strict-align archs like SPARC +// ----------------------------- +// +// GCC versions from around 4.x to to at least 13.2.0 produce worse code +// from the memcpy() method than from simple byte-by-byte shift-or code +// when reading a 32-bit integer: +// +// (1) It may be constructed on stack using using four 8-bit loads, +// four 8-bit stores to stack, and finally one 32-bit load from stack. +// +// (2) Especially with -Os, an actual memcpy() call may be emitted. +// +// This is true on at least on ARM, ARM64, SPARC, SPARC64, MIPS64EL, and +// RISC-V. Of these, ARM, ARM64, and RISC-V support unaligned access in +// some processors but not all so this is relevant only in the case when +// GCC assumes that unaligned is not supported or -mstrict-align or +// -mno-unaligned-access is used. +// +// For Clang it makes little difference. ARM64 with -O2 -mstrict-align +// was one the very few with a minor difference: the memcpy() version +// was one instruction longer. +// +// Conclusion: At least in case of GCC and Clang, byte-by-byte code is +// the best choise for strict-align archs to do unaligned access. +// +// See also: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111502 +// +// Thanks to <https://godbolt.org/> it was easy to test different compilers. +// The following is for little endian targets: +/* +#include <stdint.h> +#include <string.h> + +uint32_t bytes16(const uint8_t *b) +{ + return (uint32_t)b[0] + | ((uint32_t)b[1] << 8); +} + +uint32_t copy16(const uint8_t *b) +{ + uint16_t v; + memcpy(&v, b, sizeof(v)); + return v; +} + +uint32_t bytes32(const uint8_t *b) +{ + return (uint32_t)b[0] + | ((uint32_t)b[1] << 8) + | ((uint32_t)b[2] << 16) + | ((uint32_t)b[3] << 24); +} + +uint32_t copy32(const uint8_t *b) +{ + uint32_t v; + memcpy(&v, b, sizeof(v)); + return v; +} + +void wbytes16(uint8_t *b, uint16_t v) +{ + b[0] = (uint8_t)v; + b[1] = (uint8_t)(v >> 8); +} + +void wcopy16(uint8_t *b, uint16_t v) +{ + memcpy(b, &v, sizeof(v)); +} + +void wbytes32(uint8_t *b, uint32_t v) +{ + b[0] = (uint8_t)v; + b[1] = (uint8_t)(v >> 8); + b[2] = (uint8_t)(v >> 16); + b[3] = (uint8_t)(v >> 24); +} + +void wcopy32(uint8_t *b, uint32_t v) +{ + memcpy(b, &v, sizeof(v)); +} +*/ + + +#ifdef TUKLIB_FAST_UNALIGNED_ACCESS static inline uint16_t read16ne(const uint8_t *buf) { -#if defined(TUKLIB_FAST_UNALIGNED_ACCESS) \ - && defined(TUKLIB_USE_UNSAFE_TYPE_PUNNING) +#ifdef TUKLIB_USE_UNSAFE_TYPE_PUNNING return *(const uint16_t *)buf; #else uint16_t num; @@ -227,8 +333,7 @@ read16ne(const uint8_t *buf) static inline uint32_t read32ne(const uint8_t *buf) { -#if defined(TUKLIB_FAST_UNALIGNED_ACCESS) \ - && defined(TUKLIB_USE_UNSAFE_TYPE_PUNNING) +#ifdef TUKLIB_USE_UNSAFE_TYPE_PUNNING return *(const uint32_t *)buf; #else uint32_t num; @@ -241,8 +346,7 @@ read32ne(const uint8_t *buf) static inline uint64_t read64ne(const uint8_t *buf) { -#if defined(TUKLIB_FAST_UNALIGNED_ACCESS) \ - && defined(TUKLIB_USE_UNSAFE_TYPE_PUNNING) +#ifdef TUKLIB_USE_UNSAFE_TYPE_PUNNING return *(const uint64_t *)buf; #else uint64_t num; @@ -255,8 +359,7 @@ read64ne(const uint8_t *buf) static inline void write16ne(uint8_t *buf, uint16_t num) { -#if defined(TUKLIB_FAST_UNALIGNED_ACCESS) \ - && defined(TUKLIB_USE_UNSAFE_TYPE_PUNNING) +#ifdef TUKLIB_USE_UNSAFE_TYPE_PUNNING *(uint16_t *)buf = num; #else memcpy(buf, &num, sizeof(num)); @@ -268,8 +371,7 @@ write16ne(uint8_t *buf, uint16_t num) static inline void write32ne(uint8_t *buf, uint32_t num) { -#if defined(TUKLIB_FAST_UNALIGNED_ACCESS) \ - && defined(TUKLIB_USE_UNSAFE_TYPE_PUNNING) +#ifdef TUKLIB_USE_UNSAFE_TYPE_PUNNING *(uint32_t *)buf = num; #else memcpy(buf, &num, sizeof(num)); @@ -281,8 +383,7 @@ write32ne(uint8_t *buf, uint32_t num) static inline void write64ne(uint8_t *buf, uint64_t num) { -#if defined(TUKLIB_FAST_UNALIGNED_ACCESS) \ - && defined(TUKLIB_USE_UNSAFE_TYPE_PUNNING) +#ifdef TUKLIB_USE_UNSAFE_TYPE_PUNNING *(uint64_t *)buf = num; #else memcpy(buf, &num, sizeof(num)); @@ -294,68 +395,122 @@ write64ne(uint8_t *buf, uint64_t num) static inline uint16_t read16be(const uint8_t *buf) { -#if defined(WORDS_BIGENDIAN) || defined(TUKLIB_FAST_UNALIGNED_ACCESS) uint16_t num = read16ne(buf); return conv16be(num); -#else - uint16_t num = ((uint16_t)buf[0] << 8) | (uint16_t)buf[1]; - return num; -#endif } static inline uint16_t read16le(const uint8_t *buf) { -#if !defined(WORDS_BIGENDIAN) || defined(TUKLIB_FAST_UNALIGNED_ACCESS) uint16_t num = read16ne(buf); return conv16le(num); -#else - uint16_t num = ((uint16_t)buf[0]) | ((uint16_t)buf[1] << 8); - return num; -#endif } static inline uint32_t read32be(const uint8_t *buf) { -#if defined(WORDS_BIGENDIAN) || defined(TUKLIB_FAST_UNALIGNED_ACCESS) uint32_t num = read32ne(buf); return conv32be(num); +} + + +static inline uint32_t +read32le(const uint8_t *buf) +{ + uint32_t num = read32ne(buf); + return conv32le(num); +} + + +static inline uint64_t +read64be(const uint8_t *buf) +{ + uint64_t num = read64ne(buf); + return conv64be(num); +} + + +static inline uint64_t +read64le(const uint8_t *buf) +{ + uint64_t num = read64ne(buf); + return conv64le(num); +} + + +// NOTE: Possible byte swapping must be done in a macro to allow the compiler +// to optimize byte swapping of constants when using glibc's or *BSD's +// byte swapping macros. The actual write is done in an inline function +// to make type checking of the buf pointer possible. +#define write16be(buf, num) write16ne(buf, conv16be(num)) +#define write32be(buf, num) write32ne(buf, conv32be(num)) +#define write64be(buf, num) write64ne(buf, conv64be(num)) +#define write16le(buf, num) write16ne(buf, conv16le(num)) +#define write32le(buf, num) write32ne(buf, conv32le(num)) +#define write64le(buf, num) write64ne(buf, conv64le(num)) + #else + +#ifdef WORDS_BIGENDIAN +# define read16ne read16be +# define read32ne read32be +# define read64ne read64be +# define write16ne write16be +# define write32ne write32be +# define write64ne write64be +#else +# define read16ne read16le +# define read32ne read32le +# define read64ne read64le +# define write16ne write16le +# define write32ne write32le +# define write64ne write64le +#endif + + +static inline uint16_t +read16be(const uint8_t *buf) +{ + uint16_t num = ((uint16_t)buf[0] << 8) | (uint16_t)buf[1]; + return num; +} + + +static inline uint16_t +read16le(const uint8_t *buf) +{ + uint16_t num = ((uint16_t)buf[0]) | ((uint16_t)buf[1] << 8); + return num; +} + + +static inline uint32_t +read32be(const uint8_t *buf) +{ uint32_t num = (uint32_t)buf[0] << 24; num |= (uint32_t)buf[1] << 16; num |= (uint32_t)buf[2] << 8; num |= (uint32_t)buf[3]; return num; -#endif } static inline uint32_t read32le(const uint8_t *buf) { -#if !defined(WORDS_BIGENDIAN) || defined(TUKLIB_FAST_UNALIGNED_ACCESS) - uint32_t num = read32ne(buf); - return conv32le(num); -#else uint32_t num = (uint32_t)buf[0]; num |= (uint32_t)buf[1] << 8; num |= (uint32_t)buf[2] << 16; num |= (uint32_t)buf[3] << 24; return num; -#endif } static inline uint64_t read64be(const uint8_t *buf) { -#if defined(WORDS_BIGENDIAN) || defined(TUKLIB_FAST_UNALIGNED_ACCESS) - uint64_t num = read64ne(buf); - return conv64be(num); -#else uint64_t num = (uint64_t)buf[0] << 56; num |= (uint64_t)buf[1] << 48; num |= (uint64_t)buf[2] << 40; @@ -365,17 +520,12 @@ read64be(const uint8_t *buf) num |= (uint64_t)buf[6] << 8; num |= (uint64_t)buf[7]; return num; -#endif } static inline uint64_t read64le(const uint8_t *buf) { -#if !defined(WORDS_BIGENDIAN) || defined(TUKLIB_FAST_UNALIGNED_ACCESS) - uint64_t num = read64ne(buf); - return conv64le(num); -#else uint64_t num = (uint64_t)buf[0]; num |= (uint64_t)buf[1] << 8; num |= (uint64_t)buf[2] << 16; @@ -385,28 +535,9 @@ read64le(const uint8_t *buf) num |= (uint64_t)buf[6] << 48; num |= (uint64_t)buf[7] << 56; return num; -#endif } -// NOTE: Possible byte swapping must be done in a macro to allow the compiler -// to optimize byte swapping of constants when using glibc's or *BSD's -// byte swapping macros. The actual write is done in an inline function -// to make type checking of the buf pointer possible. -#if defined(WORDS_BIGENDIAN) || defined(TUKLIB_FAST_UNALIGNED_ACCESS) -# define write16be(buf, num) write16ne(buf, conv16be(num)) -# define write32be(buf, num) write32ne(buf, conv32be(num)) -# define write64be(buf, num) write64ne(buf, conv64be(num)) -#endif - -#if !defined(WORDS_BIGENDIAN) || defined(TUKLIB_FAST_UNALIGNED_ACCESS) -# define write16le(buf, num) write16ne(buf, conv16le(num)) -# define write32le(buf, num) write32ne(buf, conv32le(num)) -# define write64le(buf, num) write64ne(buf, conv64le(num)) -#endif - - -#ifndef write16be static inline void write16be(uint8_t *buf, uint16_t num) { @@ -414,10 +545,8 @@ write16be(uint8_t *buf, uint16_t num) buf[1] = (uint8_t)num; return; } -#endif -#ifndef write16le static inline void write16le(uint8_t *buf, uint16_t num) { @@ -425,10 +554,8 @@ write16le(uint8_t *buf, uint16_t num) buf[1] = (uint8_t)(num >> 8); return; } -#endif -#ifndef write32be static inline void write32be(uint8_t *buf, uint32_t num) { @@ -438,10 +565,8 @@ write32be(uint8_t *buf, uint32_t num) buf[3] = (uint8_t)num; return; } -#endif -#ifndef write32le static inline void write32le(uint8_t *buf, uint32_t num) { @@ -451,10 +576,8 @@ write32le(uint8_t *buf, uint32_t num) buf[3] = (uint8_t)(num >> 24); return; } -#endif -#ifndef write64be static inline void write64be(uint8_t *buf, uint64_t num) { @@ -468,10 +591,8 @@ write64be(uint8_t *buf, uint64_t num) buf[7] = (uint8_t)num; return; } -#endif -#ifndef write64le static inline void write64le(uint8_t *buf, uint64_t num) { @@ -485,6 +606,7 @@ write64le(uint8_t *buf, uint64_t num) buf[7] = (uint8_t)(num >> 56); return; } + #endif |