Inside Macintosh: PowerPC Numerics / Part 1 - The PowerPC Numerics Environment

Chapter 4 - Environmental Controls

This chapter describes the parts of the floating-point environment that you can control. The IEEE standard specifies that users should be able to control the rounding direction, floating-point exceptions, and in some instances the rounding precision. PowerPC Numerics implementations provide utilities (called environmental controls) with which you can set, clear, and test the rounding direction and floating-point exception flags. (See Parts 2 and 3 for the exact names of functions and instructions that control the floating-point environment.) This chapter describes the four rounding direction modes and the five floating-point exception flags that you can set, clear, and test in PowerPC Numerics. You should read it to learn more about the floating-point environment.

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Chapter Contents

Rounding Direction Modes

Rounding Precision

Exception Flags

Invalid Operation

Underflow

Overflow

Divide-by-Zero

Inexact