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public: swaplib: add comments

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This commit is contained in:
Alibek Omarov
2026-04-23 10:38:31 +05:00
committed by a1batross
parent 84447a5292
commit b60afd73e9
1 changed files with 26 additions and 13 deletions
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39
public/swaplib.h
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@@ -57,11 +57,12 @@ static inline void swap_field_( byte *p, int32_t size )
}
}
// this potentially breaks strict aliasing
static inline void swap_struct_( const swap_struct_def_t *def, size_t len, byte *data )
{
for( size_t i = 0; i < len; i++ )
{
if( def[i].size < 0 )
if( def[i].size < 0 ) // negative size is reserved to reference other swap defs
{
uint32_t count = def[i].count ? def[i].count : 1;
for( uint32_t j = 0; j < count; j++ )
@@ -69,25 +70,37 @@ static inline void swap_struct_( const swap_struct_def_t *def, size_t len, byte
continue;
}
if( def[i].count > 0 )
if( def[i].count > 0 ) // go over array of elements
{
for( uint32_t j = 0; j < def[i].count; j++ )
swap_field_( &data[def[i].offset + j * def[i].stride], def[i].size );
continue;
}
// process single field
swap_field_( &data[def[i].offset], def[i].size );
}
}
// do not use these macros, they will swap structs unconditionally
// you might want to use le_/be_ macros instead
#define swap_struct( swapdef, ptr ) swap_struct_(( swapdef ), sizeof( swapdef ) / sizeof( swapdef[0] ), (byte *)( ptr ))
#define swap_struct_begin( swapdef ) static swap_struct_def_t swapdef[] = {
#define swap_struct_begin( swapdef ) static swap_struct_def_t swapdef[] = {
#define swap_struct_end() }
// declare a single field
#define swap_struct_field( record, field ) { .offset = offsetof( record, field ), .size = sizeof(((record *)0)->field) },
// declare a struct, defined by another swap_struct
#define swap_struct_child( record, field, child ) { .offset = offsetof( record, field ), .size = -(int32_t)(sizeof( child ) / sizeof( child[0] )), .subdef = child },
#define swap_struct_array( record, field, cnt ) { .offset = offsetof( record, field ), .size = sizeof(((record *)0)->field[0]), .count = cnt, .stride = sizeof(((record *)0)->field[0]) },
// declare an array of fields, doesn't work with flexible array members
#define swap_struct_array( record, field, cnt ) { .offset = offsetof( record, field ), .size = sizeof(((record *)0)->field[0]), .count = cnt, .stride = sizeof(((record *)0)->field[0]) },
// combined swap_struct_child and swap_struct_array
#define swap_struct_array_child( record, field, child, cnt ) { .offset = offsetof( record, field ), .size = -(int32_t)(sizeof( child ) / sizeof( child[0] )), .subdef = child, .count = cnt, .stride = sizeof(((record *)0)->field[0]) },
#define swap_struct_end() }
// this is done in macros so we can completely avoid defining this
// in little endian targets
@@ -104,9 +117,16 @@ static inline void swap_struct_( const swap_struct_def_t *def, size_t len, byte
#define le_struct_child( x, y, z )
#define le_struct_array( x, y, z )
#define le_struct_array_child( x, y, z, w )
#define le_struct_end()
#define le_struct_end() extern int _le_struct_end_dummy // define as extern variable, to let end() end with ;
#define le_struct_swap( x, y ) (void)(y)
#else
#define be_struct_begin( x )
#define be_struct_field( x, y )
#define be_struct_child( x, y, z )
#define be_struct_array( x, y, z )
#define be_struct_array_child( x, y, z, w )
#define be_struct_end() extern int _le_struct_end_dummy
#define be_struct_swap( x, y ) (void)(y)
#define le_struct_begin( x ) swap_struct_begin( x )
#define le_struct_field( x, y ) swap_struct_field( x, y )
#define le_struct_child( x, y, z ) swap_struct_child( x, y, z )
@@ -114,13 +134,6 @@ static inline void swap_struct_( const swap_struct_def_t *def, size_t len, byte
#define le_struct_array_child( x, y, z, w ) swap_struct_array_child( x, y, z, w )
#define le_struct_end() swap_struct_end()
#define le_struct_swap( x, y ) swap_struct( x, y )
#define be_struct_begin( x )
#define be_struct_field( x, y )
#define be_struct_child( x, y, z )
#define be_struct_array( x, y, z )
#define be_struct_array_child( x, y, z, w )
#define be_struct_end()
#define be_struct_swap( x, y ) (void)(y)
#endif