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author | Max Horn | 2006-02-25 11:45:56 +0000 |
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committer | Max Horn | 2006-02-25 11:45:56 +0000 |
commit | 1c93f7bcead228faebc0c79bc31c038de8c26016 (patch) | |
tree | e65a06c3740b71e6d1f098010c672e1dd29857e7 | |
parent | 1f987027f8f901e48f064cdc766064f4bf4b6fc9 (diff) | |
download | scummvm-rg350-1c93f7bcead228faebc0c79bc31c038de8c26016.tar.gz scummvm-rg350-1c93f7bcead228faebc0c79bc31c038de8c26016.tar.bz2 scummvm-rg350-1c93f7bcead228faebc0c79bc31c038de8c26016.zip |
Removed the obsolete MKID macro; added some doxygen comments, in particular for MKID_BE
svn-id: r20873
-rw-r--r-- | common/endian.h | 51 |
1 files changed, 38 insertions, 13 deletions
diff --git a/common/endian.h b/common/endian.h index 4e1f46c026..c3ff673235 100644 --- a/common/endian.h +++ b/common/endian.h @@ -29,6 +29,10 @@ // Endian conversion functions, macros etc., follow from here! // +/** + * Swap the bytes in a 32 bit word in order to convert LE encoded data to BE + * and vice versa. + */ FORCEINLINE uint32 SWAP_BYTES_32(uint32 a) { return ((a >> 24) & 0x000000FF) | ((a >> 8) & 0x0000FF00) | @@ -36,26 +40,46 @@ FORCEINLINE uint32 SWAP_BYTES_32(uint32 a) { ((a << 24) & 0xFF000000); } +/** + * Swap the bytes in a 16 bit word in order to convert LE encoded data to BE + * and vice versa. + */ FORCEINLINE uint16 SWAP_BYTES_16(uint16 a) { return ((a >> 8) & 0x00FF) + ((a << 8) & 0xFF00); } -#if defined(SCUMM_LITTLE_ENDIAN) +/** + * A wrapper macro used around four character constants, like 'DATA', to + * ensure portability. Typical usage: MKID_BE('DATA'). + * + * Why is this necessary? The C/C++ standard does not define the endianess to + * be used for character constants. Hence if one uses multi-byte character + * constants, a potential portability problem opens up. + * + * Fortunately, a semi-standard has been established: On almost all systems + * and compilers, multi-byte character constants are encoded using the big + * endian convention (probably in analogy to the encoding of string constants). + * Still some systems differ. This is why we provide the MKID_BE macro. If + * you wrap your four character constants with it, the result will always be + * BE encoded, even on systems which differ from the default BE encoding. + * + * For the latter systems we provide the INVERSE_MKID override. + */ +#if defined(INVERSE_MKID) +#define MKID_BE(a) ((uint32) \ + (((a) >> 24) & 0x000000FF) | \ + (((a) >> 8) & 0x0000FF00) | \ + (((a) << 8) & 0x00FF0000) | \ + (((a) << 24) & 0xFF000000)) + +#else +# define MKID_BE(a) ((uint32)(a)) +#endif - #define PROTO_MKID(a) ((uint32) \ - (((a) >> 24) & 0x000000FF) | \ - (((a) >> 8) & 0x0000FF00) | \ - (((a) << 8) & 0x00FF0000) | \ - (((a) << 24) & 0xFF000000)) - #if defined(INVERSE_MKID) - # define MKID(a) ((uint32)(a)) - # define MKID_BE(a) PROTO_MKID(a) - #else - # define MKID(a) PROTO_MKID(a) - # define MKID_BE(a) ((uint32)(a)) - #endif + +#if defined(SCUMM_LITTLE_ENDIAN) #define READ_UINT16(a) READ_LE_UINT16(a) #define READ_UINT32(a) READ_LE_UINT32(a) @@ -96,6 +120,7 @@ FORCEINLINE uint16 SWAP_BYTES_16(uint16 a) { #error No endianness defined + #endif |