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Fixed invalid cast and unaligned memory access

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Although acceptible to Intel CPUs, it's still undefined behaviour according to the C++ standard.

It can be replaced with memcpy, which makes the code simpler, and it generates the same assembly code with gcc and clang with -O2 (verified with godbolt).

Also expanded the test to include other little endian CPUs by testing for __LITTLE_ENDIAN__.
This commit is contained in:
Sean McBride 2023-06-02 10:57:28 -04:00
parent 5330112f05
commit 57da72d444
1 changed files with 20 additions and 13 deletions
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33
modules/core/src/persistence.cpp
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@ -295,16 +295,20 @@ int decodeSimpleFormat( const char* dt )
}
#if defined __i386__ || defined(_M_IX86) || defined __x86_64__ || defined(_M_X64)
#define CV_UNALIGNED_LITTLE_ENDIAN_MEM_ACCESS 1
#if defined __i386__ || defined(_M_IX86) || defined __x86_64__ || defined(_M_X64) || \
(defined (__LITTLE_ENDIAN__) && __LITTLE_ENDIAN__)
#define CV_LITTLE_ENDIAN_MEM_ACCESS 1
#else
#define CV_UNALIGNED_LITTLE_ENDIAN_MEM_ACCESS 0
#define CV_LITTLE_ENDIAN_MEM_ACCESS 0
#endif
static inline int readInt(const uchar* p)
{
#if CV_UNALIGNED_LITTLE_ENDIAN_MEM_ACCESS
return *(const int*)p;
// On little endian CPUs, both branches produce the same result. On big endian, only the else branch does.
#if CV_LITTLE_ENDIAN_MEM_ACCESS
int val;
memcpy(&val, p, sizeof(val));
return val;
#else
int val = (int)(p[0] | (p[1] << 8) | (p[2] << 16) | (p[3] << 24));
return val;
@ -313,8 +317,11 @@ static inline int readInt(const uchar* p)
static inline double readReal(const uchar* p)
{
#if CV_UNALIGNED_LITTLE_ENDIAN_MEM_ACCESS
return *(const double*)p;
// On little endian CPUs, both branches produce the same result. On big endian, only the else branch does.
#if CV_LITTLE_ENDIAN_MEM_ACCESS
double val;
memcpy(&val, p, sizeof(val));
return val;
#else
unsigned val0 = (unsigned)(p[0] | (p[1] << 8) | (p[2] << 16) | (p[3] << 24));
unsigned val1 = (unsigned)(p[4] | (p[5] << 8) | (p[6] << 16) | (p[7] << 24));
@ -326,9 +333,9 @@ static inline double readReal(const uchar* p)
static inline void writeInt(uchar* p, int ival)
{
#if CV_UNALIGNED_LITTLE_ENDIAN_MEM_ACCESS
int* ip = (int*)p;
*ip = ival;
// On little endian CPUs, both branches produce the same result. On big endian, only the else branch does.
#if CV_LITTLE_ENDIAN_MEM_ACCESS
memcpy(p, &ival, sizeof(ival));
#else
p[0] = (uchar)ival;
p[1] = (uchar)(ival >> 8);
@ -339,9 +346,9 @@ static inline void writeInt(uchar* p, int ival)
static inline void writeReal(uchar* p, double fval)
{
#if CV_UNALIGNED_LITTLE_ENDIAN_MEM_ACCESS
double* fp = (double*)p;
*fp = fval;
// On little endian CPUs, both branches produce the same result. On big endian, only the else branch does.
#if CV_LITTLE_ENDIAN_MEM_ACCESS
memcpy(p, &fval, sizeof(fval));
#else
Cv64suf v;
v.f = fval;