nerdcruft/libcruft-util
1
0
Fork 0
Code Issues Releases Activity

endian: add float byteswap specialisation

Browse Source
This commit is contained in:
Danny Robson 2017-10-12 17:36:46 +11:00
parent aff4786409
commit d8bb00c9c3
3 changed files with 58 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
CMakeLists.txt
View File

@ -495,6 +495,7 @@ if (TESTS)
crypto/tea
crypto/xtea
crypto/xxtea
endian
exe
extent
fixed

33
endian.hpp
View File

@ -33,7 +33,7 @@ namespace util {
//-------------------------------------------------------------------------
template <typename T>
constexpr T
bswap (T);
bswap (T) noexcept;
// CXX: Update using "if constexpr" when available. It doesn't seem to be
// worth the dicking about to use enable_if_t to differentiate the
@ -42,7 +42,7 @@ namespace util {
template <> \
constexpr \
int##S##_t \
bswap (int##S##_t v) { \
bswap (int##S##_t v) noexcept { \
const union { \
int##S##_t s; \
uint##S##_t u; \
@ -55,12 +55,31 @@ namespace util {
SIGNED_BSWAP(32)
SIGNED_BSWAP(64)
template <> constexpr int8_t bswap ( int8_t v) { return v; }
template <> constexpr uint8_t bswap (uint8_t v) { return v; }
template <> constexpr int8_t bswap ( int8_t v) noexcept { return v; }
template <> constexpr uint8_t bswap (uint8_t v) noexcept { return v; }
template <> constexpr uint16_t bswap (uint16_t v) { return __builtin_bswap16 (v); }
template <> constexpr uint32_t bswap (uint32_t v) { return __builtin_bswap32 (v); }
template <> constexpr uint64_t bswap (uint64_t v) { return __builtin_bswap64 (v); }
template <> constexpr uint16_t bswap (uint16_t v) noexcept { return __builtin_bswap16 (v); }
template <> constexpr uint32_t bswap (uint32_t v) noexcept { return __builtin_bswap32 (v); }
template <> constexpr uint64_t bswap (uint64_t v) noexcept { return __builtin_bswap64 (v); }
// use a type-punning union to punt the byte swapping operation to the
// unsigned integer code.
//
// this is debatably safe under production compilers like gcc + clang
// despite what the standard may say about unions.
template <>
constexpr float
bswap (float v) noexcept
{
union {
float f;
uint32_t u;
} temp { .f = v };
temp.u = bswap (temp.u);
return temp.f;
}
//-------------------------------------------------------------------------

31
test/endian.cpp Normal file
View File

@ -0,0 +1,31 @@
#include "tap.hpp"
#include "endian.hpp"
///////////////////////////////////////////////////////////////////////////////
int
main (void)
{
util::TAP::logger tap;
{
uint32_t a = 0x12345678, b = 0x78563412;
tap.expect_eq (a, util::bswap (b), "u32 byteswap");
}
{
// try to byte swap the pattern for 1.0f
//
// it may not be the most robust test, but it'll catch the most
// egregious errors for the time being.
union {
uint32_t u;
float f;
} data { .u = 0x0000803f /* 0x3f800000 == 1.f */ };
tap.expect_eq (util::bswap (data.f), 1.f, "f32 byteswap");
};
return tap.status ();
}