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Full Discussion: help with data type sizes
Top Forums Programming help with data type sizes Post 302488038 by DGPickett on Friday 14th of January 2011 04:44:54 PM
Old 01-14-2011
When loading phydsical accumulators and registers with numbers, they are stretched to fit, with zeros if unsigned or by repeating the sign bit at the high order bit of the comp-2 representation. Similarly, C stretches the values to the bigger type to compare or compute.

Usually, a char is 1 byte unsigned (0-255), and an int is 4 bytes signed (+/- 2 billion plus). Old C models had int and short at 2 and long at 4, most 32 bit models have int and long at 4, and long models have int at 4 and long at 8.

Floating types are particularly variable in computers, but in C it is 4 bytes, and there is an IEEE spec on floating numbers that makes them portable. Differnt float types are 64 Double or 80 Long Double or is it Double Double, no, that feels wrong, bits. Float has some bits for mantissa, usually as a 2's complement fraction between .5 and < 1.0 when normalized, where 010000- is 1/2, and exponent, usually a 2's complement power of 2 but sometimes a 2's complement power of 16 or an "excess" number, where the boundary between negative and positive is shifted to a more useful range. None of this leaks into IEEE floating representations.

C increments pointers for each type by its size. types.h gives a lot of info on alternative C types. Some APIs just typedef their int types int1, int2, int4 and int8 or unsigned uint1, uint2, uint4, uint8.

Positions of items in a struct are usualy formatted #pragma pack 4 by default, and generally, you can save space by declaring like sized types adjacent.
Last edited by DGPickett; 01-14-2011 at 05:57 PM..
 

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LEARN ABOUT XFREE86

values

values.h(3HEAD) 						      Headers							   values.h(3HEAD)

NAME

       values.h, values - machine-dependent values

SYNOPSIS

       #include <values.h>

DESCRIPTION

       This file contains a set of manifest constants, conditionally defined for particular processor architectures.

       The  model  assumed  for  integers  is binary representation (one's or two's complement), where the sign is represented by the value of the
       high-order bit.

       BITS(type)		       The number of bits in a specified type (for example, int).

       HIBITS			       The value of a short integer with only the high-order bit set.

       HIBITL			       The value of a long integer with only the high-order bit set.

       HIBITI			       The value of a regular integer with only the high-order bit set.

       MAXSHORT 		       The maximum value of a signed short integer.

       MAXLONG			       The maximum value of a signed long integer.

       MAXINT			       The maximum value of a signed regular integer.

       MAXFLOAT, LN_MAXFLOAT	       The maximum value of a single-precision floating-point number, and its natural logarithm.

       MAXDOUBLE, LN_MAXDOUBLE	       The maximum value of a double-precision floating-point number, and its natural logarithm.

       MINFLOAT, LN_MINFLOAT	       The minimum positive value of a single-precision floating-point number, and its natural logarithm.

       MINDOUBLE, LN_MINDOUBLE	       The minimum positive value of a double-precision floating-point number, and its natural logarithm.

       FSIGNIF			       The number of significant bits in the mantissa of a single-precision floating-point number.

       DSIGNIF			       The number of significant bits in the mantissa of a double-precision floating-point number.

SEE ALSO

       intro(3) math.h(3HEAD)

SunOS 5.10							    2 Mar 1993							   values.h(3HEAD)
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