Floating-Point IP Cores User Guide

ID 683750
Date 9/13/2021
Document Table of Contents

1.7. Non-IEEE-754 Standard Format

Only the ALTFP_CONVERT and FP_FUNCTIONS Intel FPGA IP (when the convert function is selected) support the fixed point format.

The fixed-point data type is similar to the conventional integer data type, except that the fixed-point data carries a predetermined number of fractional bits. If the width of the fraction is 0, the data becomes a normal signed integer.

The notation for fixed-point format numbers in this user guide is Qm.f, where Q designates that the number is in Q format notation, m is the number of bits used to indicate the integer portion of the number, and f is the number of bits used to indicate the fractional portion of the number.

For example, Q4.12 describes a number with 4 integer bits and 12 fractional bits in a 16-bit word.

The following figures show the difference between the signed-integer format and the fixed-point format for a 32-bit number.

Figure 12. Signed-Integer Format
Figure 13. Fixed-Point Format

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