Inside Macintosh: PowerPC Numerics / Part 3 - Numerics in PowerPC Assembly Language

Chapter 12 - Assembly-Language Environmental Controls

This chapter describes how to use assembly-language instructions to control the floating-point environment (rounding direction and exception flags) described in Chapter 4, "Environmental Controls." The current state of the floating-point environment is stored in the Floating-Point Status and Control Register and summarized in the Condition Register. This chapter describes exactly how these two registers store the environment. Then it describes the PowerPC assembler instructions you can use to test or change the environment.

Read this chapter to learn how to access and manipulate the floating-point environment in assembly language or to learn how the PowerPC architecture stores the floating-point environment.

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Chapter Contents

The Floating-Point Environment

The Floating-Point Status and Control Register

The Condition Register

Inquiries: Class and Sign

Floating-Point Result Flags and Condition Codes

Example: Determining Class

Setting the Rounding Direction

Floating-Point Exceptions

Exception Bits in the FPSCR

Signaling and Clearing Floating-Point Exceptions

Enabling and Disabling Floating-Point Exceptions

Testing for Floating-Point Exceptions

Saving and Restoring the Floating-Point Environment