F.2 Data Representations

Bit numbering of any given data element depends on the architecture in use: SPARCstation machines use bit 0 as the least significant bit, with byte 0 being the most significant byte. The tables in this section describe the various representations.

F.2.1 Integer Representations

Integer types used in ISO C are short, int, long, and long long:

Table F-2 Representation of short

Table F-3 Representation of int

Table F-4 Representation of long Compiled with -m32

Table F-5 Representation of long (-m64) and long long (both -m32 and -m64)

F.2.2 Floating-Point Representations

float, double, and long double data elements are represented according to the ISO IEEE 754-1985 standard. The representation is:

(-1)^s *2^{(e - bias)} *[j.f]

where:

• s is the sign

• e is the biased exponent

• j is the leading bit, determined by the value of e. In the case of long double (x86), the leading bit is explicit; in all other cases, it is implicit.

• f = fraction

• u means that the bit can be either 0 or 1 (used in the tables in this section).

For IEEE Single and Double, j is always implicit. When the biased exponent is 0, j is 0, and the resulting number is subnormal as long as f is not 0. When the biased exponent is greater than 0, j is 1 as long as the number is finite.

For Intel 80–bit Extended, j is always explicit.

The following tables show the position of the bits.

Table F-6 float Representation

Table F-7 double Representation

Table F-8 long double Representation (SPARC)

Table F-9 long double Representation (x86)

For further information, refer to the Numerical Computation Guide.

F.2.3 Exceptional Values

float and double numbers are said to contain a “hidden,” or implied, bit, providing for one more bit of precision than would otherwise be the case. In the case of long double, the leading bit is implicit (SPARC) or explicit (x86); this bit is 1 for normal numbers, and 0 for subnormal numbers.

Table F-10 float Representations

Table F-11 double Representations

Table F-12 long double Representations

F.2.4 Hexadecimal Representation of Selected Numbers

The following tables show the hexadecimal representations.

Table F-13 Hexadecimal Representation of Selected Numbers (SPARC)

Table F-14 Hexadecimal Representation of Selected Numbers (x86)

For further information, refer to the Numerical Computation Guide.

F.2.5 Pointer Representation

A pointer in C occupies four bytes. A pointer in C occupies 8 bytes on 64–bit SPARC v9 architectures. The NULL value pointer is equal to zero.

F.2.6 Array Storage

Arrays are stored with their elements in a specific storage order. The elements are actually stored in a linear sequence of storage elements.

C arrays are stored in row-major order. The last subscript in a multidimensional array varies the fastest.

String data types are arrays of char elements. The maximum number of characters allowed in a string literal or wide string literal (after concatenation) is 4,294,967,295.

See F.1 Storage Allocation for information on the size limit of storage allocated on the stack.

Table F-15 Array Types and Storage

Static and global arrays can accommodate many more elements.

F.2.7 Arithmetic Operations on Exceptional Values

This section describes the results derived from applying the basic arithmetic operations to combinations of exceptional and ordinary floating-point values. The information that follows assumes that no traps or any other exception actions are taken.

The following table explains the abbreviations.

Table F-16 Abbreviation Usage

The following tables describe the types of values that result from arithmetic operations performed with combinations of different types of operands.

Table F-17 Addition and Subtraction Results

¹Num + Num could be Inf, rather than Num, when the result is too large (overflow). Inf + Inf = NaN when the infinities are of opposite sign.

Table F-18 Multiplication Results

Table F-19 Division Results

Table F-20 Comparison Results