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Libraries and Floating Point Support Guide

Preface The ARM C and C++ Libraries The ARM C Micro-library Floating-point Support About floating-point support The software floating-point library, fplib Calling fplib routines fplib arithmetic on numbers in a particular format fplib conversions between floats, long longs, doub fplib comparisons between floats and doubles fplib C99 functions Controlling the ARM floating-point environment Floating-point functions for compatibility with Mi C99-compatible functions for controlling the ARM f C99 rounding mode and floating-point exception mac Exception flag handling Functions for handling rounding modes Functions for saving and restoring the whole float Functions for temporarily disabling exceptions ARM floating-point compiler extensions to the C99 Writing a custom exception trap handler Example of a custom exception handler Exception trap handling by signals mathlib double and single-precision floating-point IEEE 754 arithmetic Basic data types for IEEE 754 arithmetic Single precision data type for IEEE 754 arithmetic Double precision data type for IEEE 754 arithmetic Sample single precision floating-point values for Sample double precision floating-point values for IEEE 754 arithmetic and rounding Exceptions arising from IEEE 754 floating-point ar Exception types recognized by the ARM floating-poi Using the Vector Floating-Point (VFP) support libr The C and C++ Library Functions reference Floating-point Support Functions Reference

Double precision data type for IEEE 754 arithmetic

3.5.3 Double precision data type for IEEE 754 arithmetic

A double value is 64 bits wide.

The structure is:
Figure 3-2 IEEE 754 double-precision floating-point format
IEEE 754 double-precision floating-point format

As with single-precision float data types, S is the sign, Exp the exponent, and Frac the fraction. Most of the detail of float values remains true for double values, except that:
  • The Exp field is biased by 0x3FF (1023) instead of 0x7F, so numbers between 1.0 and 2.0 have an Exp field of 0x3FF.
  • The Exp value representing infinity and NaNs is 0x7FF (2047) instead of 0xFF.
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