From 374bb459369d47f598d1b07f6237f24abd0d52c6 Mon Sep 17 00:00:00 2001 From: Mark Wooding Date: Sat, 26 May 2018 16:32:01 +0100 Subject: [PATCH] utils/bits.h: Add macros for swapping endianness in place. Many processors and compilers provide handy instructions for doing this, and it's a handy primitive for loading and storing. The HTOLw etc. macros turn out to be remarkably slippery to define. It's unfortunately nonsensical to speak about an integer value having an endianness. --- utils/bits.3 | 96 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ utils/bits.h | 97 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 193 insertions(+) diff --git a/utils/bits.3 b/utils/bits.3 index 7eb1e2b..7b1c715 100644 --- a/utils/bits.3 +++ b/utils/bits.3 @@ -95,6 +95,23 @@ bits \- portable bit manipulation macros .\" @ROL64_ .\" @ROR64_ .\" +.\" ENDSWAP16 +.\" ENDSWAP32 +.\" ENDSWAP64 +.\" +.\" BTOH16 +.\" LTOH16 +.\" HTOB16 +.\" HTOL16 +.\" BTOH32 +.\" LTOH32 +.\" HTOB32 +.\" HTOL32 +.\" BTOH64 +.\" LTOH64 +.\" HTOB64 +.\" HTOL64 +.\" .\" @GETBYTE .\" @PUTBYTE .\" @@ -370,6 +387,85 @@ left or right, respectively, by .I n places. . +.SS "Byte order conversions" +For each size suffix +.IR w , +the macro invocation +.BI ENDSWAP w ( x ) +returns the +.IR w -bit +value +.IR x +with its bytes reversed. The +.B ENDSWAP8 +macro does nothing (except truncate its operand to 8 bits), but is +provided for the sake of completeness. +.PP +A +.I big-endian +representation stores the most significant octet of an integer at the +lowest address, with the following octets in decreasing order of +significance. A +.I little-endian +representation instead stores the +.I least +significant octet at the lowest address, with the following octets in +increasing order of significance. An environment has a preferred order +for arranging the constituent octets of an integer of some given size in +memory; this might be either the big- or little-endian representation +just described, or something else strange. +.PP +It might be possible to rearrange the bits in an integer so that, when +that integer is stored to memory in the environment's preferred manner, +you end up with the big- or little-endian representation of the original +integer; and, similarly, it might be possible to load a big- or +little-endian representation of an integer into a variable using the +environment's preferred ordering and then rearrange the bits so as to +recover the integer value originally represented. If the environment is +sufficiently strange, these things might not be possible, but this is +actually quite rare. +.PP +Say that an integer has been converted to +.I big- +or +.I "little-endian form" +if, when it is stored in memory in the environment's preferred manner, +one ends up with a big- or little-endian representation of the original +integer. Equivalently, if one starts with a big- or little-endian +representation of some integer, and loads it into a variable using the +environment's preferred manner, one ends up with the big- or +little-endian form of the original integer. +.PP +If these things are possible, then the following macros are defined. +.TP +.BI HTOL w ( x ) +Convert a +.IR w -bit +integer +.I x +to little-endian form. +.TP +.BI HTOB w ( x ) +Convert a +.IR w -bit +integer +.I x +to big-endian form. +.TP +.BI LTOH w ( x ) +Convert a +.IR w -bit +integer +.I x +from little-endian form. +.TP +.BI BTOH w ( x ) +Convert a +.IR w -bit +integer +.I x +from big-endian form. +. .SS "Load and store" The macro invocation .BI GETBYTE( p ", " o ) diff --git a/utils/bits.h b/utils/bits.h index 4279170..3b12f96 100644 --- a/utils/bits.h +++ b/utils/bits.h @@ -314,6 +314,103 @@ typedef unsigned char octet, uint8; } while (0) #endif +/* --- Endianness swapping --- */ + +#ifndef ENDSWAP8 +# define ENDSWAP8(x) U8(x) +#endif +#ifndef ENDSWAP16 +# define ENDSWAP16(x) \ + ((((uint16)(x) >> 8)&0xff) | \ + (((uint16)(x)&0xff) << 8)) +#endif +#ifndef ENDSWAP24 +# define ENDSWAP24(x) \ + ((((uint24)(x) >> 16)&0xff) | \ + ((uint24)(x)&0xff00) | \ + ((uint24)((x)&0xff) << 16)) +#endif +#ifndef ENDSWAP32 +# define ENDSWAP32(x) \ + (ENDSWAP16(((uint32)(x) >> 16)&0xffff) | \ + ((uint32)ENDSWAP16((x)&0xffff) << 16)) +#endif +#if defined(HAVE_UINT64) && !defined(ENDSWAP64) +# define ENDSWAP64(x) \ + (ENDSWAP32(((uint64)(x) >> 32)&0xffffffff) | \ + ((uint64)ENDSWAP32((x)&0xffffffff) << 32)) +#endif +#ifdef HAVE_UINT64 +# define ENDSWAP64_(z, x) \ + ((z).i = ENDSWAP64((x).i)) +#else +# define ENDSWAP64_(z, x) \ + ((z).lo = ENDSWAP32((x).hi), \ + (z).hi = ENDSWAP32((x).lo)) +#endif + +#define MLIB_LITTLE_ENDIAN 1234 +#define MLIB_BIG_ENDIAN 4321 +#if defined(__ORDER_LITTLE_ENDIAN__) && \ + __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__ +# define MLIB_BYTE_ORDER MLIB_LITTLE_ENDIAN +#elif defined(__ORDER_BIG_ENDIAN__) && \ + __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__ +# define MLIB_BYTE_ORDER MLIB_BIG_ENDIAN +#endif + +#if MLIB_BYTE_ORDER == MLIB_LITTLE_ENDIAN +# define HTOL16(x) (x) +# define LTOH16(x) (x) +# define HTOB16(x) ENDSWAP16(x) +# define BTOH16(x) ENDSWAP16(x) +# define HTOL24(x) (x) +# define LTOH24(x) (x) +# define HTOB24(x) ENDSWAP24(x) +# define BTOH24(x) ENDSWAP24(x) +# define HTOL32(x) (x) +# define LTOH32(x) (x) +# define HTOB32(x) ENDSWAP32(x) +# define BTOH32(x) ENDSWAP32(x) +# ifdef HAVE_UINT64 +# define HTOL64(x) (x) +# define LTOH64(x) (x) +# define HTOB64(x) ENDSWAP64(x) +# define BTOH64(x) ENDSWAP64(x) +# endif +# define HTOL64_(z, x) ASSIGN64(z, x) +# define LTOH64_(z, x) ASSIGN64(z, x) +# define HTOB64_(z, x) ENDSWAP64_(z, x) +# define BTOH64_(z, x) ENDSWAP64_(z, x) +#elif MLIB_BYTE_ORDER == MLIB_BIG_ENDIAN +# define HTOL16(x) ENDSWAP16(x) +# define LTOH16(x) ENDSWAP16(x) +# define HTOB16(x) (x) +# define BTOH16(x) (x) +# define HTOL24(x) ENDSWAP24(x) +# define LTOH24(x) ENDSWAP24(x) +# define HTOB24(x) (x) +# define BTOH24(x) (x) +# define HTOL32(x) ENDSWAP32(x) +# define LTOH32(x) ENDSWAP32(x) +# define HTOB32(x) (x) +# define BTOH32(x) (x) +# ifdef HAVE_UINT64 +# define HTOL64(x) ENDSWAP64(x) +# define LTOH64(x) ENDSWAP64(x) +# define HTOB64(x) (x) +# define BTOH64(x) (x) +# define HTOL64_(z, x) ENDSWAP64_(z, x) +# define LTOH64_(z, x) ENDSWAP64_(z, x) +# define HTOB64_(z, x) ((z).i = (x).i) +# define BTOH64_(z, x) ((z).i = (x).i) +# endif +# define HTOL64_(z, x) ENDSWAP64_(z, x) +# define LTOH64_(z, x) ENDSWAP64_(z, x) +# define HTOB64_(z, x) ASSIGN64(z, x) +# define BTOH64_(z, x) ASSIGN64(z, x) +#endif + /* --- Storage and retrieval --- */ #define GETBYTE(p, o) (((octet *)(p))[o] & MASK8) -- 2.11.0