[Zlib-devel] crc32 big/little endian

[Mark Adler]

On Apr 21, 2010, at 11:53 PM, Vincent Torri wrote:
> C ANSI (C89) specifies:
> 
> sizeof(char) = 1
> 
> sizeof(char) <= sizeof(short) <= sizeof(int) <= sizeof(long)
> 
> and no change with signed or unsigned
> 
> that's all.

No, that's not all.  Minimum sizes are specified in C89.  See below: "Their implementation-defined values shall be equal or greater in magnitude (absolute value) to those shown".  Also K&R 2nd edition (the ANSI C edition) says basically the same thing: "longs are at least 32 bits".

I can't find my K&R 1st edition to see what it says about that.

In any case the constraints are bits(char) <= bits(short) <= bits(int) <= bits(long), 8 <= bits(char), 16 <= bits(short), and 32 <= bits(long).  zlib makes only those assumptions about char, short, int, and long (and their unsigned counterparts).

Mark



2.2.4.2 Numerical limits

   A conforming implementation shall document all the limits specified
in this section, which shall be specified in the headers <limits.h>
and <float.h> .

"Sizes of integral types <limits.h>"

   The values given below shall be replaced by constant expressions
suitable for use in #if preprocessing directives.  Their
implementation-defined values shall be equal or greater in magnitude
(absolute value) to those shown, with the same sign.

 * maximum number of bits for smallest object that is not a bit-field (byte) 
CHAR_BIT                         8 

 * minimum value for an object of type signed char 
SCHAR_MIN                     -127 

 * maximum value for an object of type signed char 
SCHAR_MAX                     +127 

 * maximum value for an object of type unsigned char 
UCHAR_MAX                      255 

 * minimum value for an object of type char 
CHAR_MIN                     see below 

 * maximum value for an object of type char 
CHAR_MAX                     see below 

 * maximum number of bytes in a multibyte character, for any supported locale 
MB_LEN_MAX                       1 

 * minimum value for an object of type short int 
SHRT_MIN                    -32767 

 * maximum value for an object of type short int 
SHRT_MAX                    +32767 

 * maximum value for an object of type unsigned short int 
USHRT_MAX                    65535 

 * minimum value for an object of type int 
INT_MIN                     -32767 

 * maximum value for an object of type int 
INT_MAX                     +32767 

 * maximum value for an object of type unsigned int 
UINT_MAX                     65535 

 * minimum value for an object of type long int 
LONG_MIN               -2147483647 

 * maximum value for an object of type long int 
LONG_MAX               +2147483647 

 * maximum value for an object of type unsigned long int 
ULONG_MAX               4294967295