HP aC++/HP ANSI C Release Notes (B3901-90037; A.06.26; September 2011)

• In next release, default C compilation mode will change from C89 to C99

• In next release, default C++ compilation mode changes to full -AA

Decimal floating-point arithmetic (HP-UX 11.31 only) (New)

On HP-UX 11.31 systems, support is now included for decimal floating-point arithmetic

for C. This support follows the current draft revision of the IEEE 754 floating-point standard

and ISO/IEC Technical Report 24732, Extensions for the programming language C to

support decimal floating-point arithmetic. With decimal FP (unlike the usual binary FP),

typical numerical strings can be represented exactly in the types, avoiding subtle input

errors and confusion from inexact output. Therefore, decimal FP is WYSIWYG.

Decimal FP is designed particularly for financial applications, including banking, billing,

tax calculation, currency exchange, and accounting.

A decimal FP representation is best thought of as a triple (s, c, q) composed of a sign (1

or −1), an integral coefficient, and a quantum exponent, representing s * c *10

Therefore, 123. = (1, 123, 0) and 123.00 = (1, 12300, −2) are different representations,

although they have the same numerical value and compare equal. Arithmetic operations

are defined to preserve the position of the decimal point, much as hand-computation

would. For example, 123.00 + 45.6 = 168.60 and 123.00 * 0.01 = 1.2300. These

special quantum semantics facilitate exact fix-point calculation. For typical floating-point

calculations, the quantum semantics can be ignored.

Decimal FP support includes the following:

• Three built-in decimal FP types:

_Decimal32 _Decimal64 _Decimal128

with 7, 16, and 34 decimal digits of precision, respectively.

• The usual built-in arithmetic operators for decimal FP operands: +, −, *, /,

assignments, comparisons, and conversions with integer and binary FP types, all

with correctly-rounded IEEE arithmetic. An operation may combine a decimal FP

operand with an operand of a different decimal FP type or with an integer type.

However, mixing operands of decimal and binary FP types is not allowed.

• 60 math functions for each decimal FP type. Function suffixes are d32 for

_Decimal32, d64 for _Decimal64, and d128 for _Decimal128. Included are:

◦ Decimal FP versions of the C99 math functions.

◦ New functions to manage quantum exponents (for fixed-point calculation).

◦ Routines to encode and decode data for either of the two standard encodings

for decimal FP data. Details of the encodings are in the draft revision of IEEE

754, which refers to them as the "binary encoding", which the HP C/aC++

24 Product changes in earlier versions