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C166 User's Guide

FLOAT64 Compiler Directive

Abbreviation F64
Arguments None.
Default 32-bit floating-point math is used.
µVision Options — C166 — Double-precision Floating-point.
Description 

The FLOAT64 directive enables 64-bit (double-precision) floating-point math for double variable types in your C programs. Variables of type float continue to use 32-bit floating-point math.

By default, all floating-point math is performed using 32-bits (even when the double type is specified.) The FLOAT64 directive must be specified to use 64-bit floating-point math.

Example 
C166 SAMPLE.C FLOAT64

#pragma float64