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[avr-gcc-list] Double desirability

From: James A.R. Koehler
Subject: [avr-gcc-list] Double desirability
Date: Tue, 05 Apr 2005 13:12:21 -0700
User-agent: Mozilla Thunderbird 1.0 (X11/20041206)

I just want to put in my two-cents worth in support of having a decent double library for the AVR. Doubles are not just useful in desktop machines but also are required more and more frequently in embedded systems. I do RF design and most, perhaps all, modern DDS (direct digital sysnthesis) chips have 48-bit (often larger!) phase registers and so to set frequencies, one must be able to do 64-bit operations.

A few years ago, I wrote a program using one of these DDS chips in AVR-GCC and was astonished to see that the code size went up enormously in integer operations when I went from 32-bit variables to 64-bit ones. I eventually wrote my own small library to do 64-bit integer multiplies and divides. I don't know if the current library routines are any better. In terms of program size, a 64-bit multiply or divide shouldn't take significantly more code space than a 32-bit one - it will just run a factor of two slower.

I don't know much about compiler design but if there is any way I can help in producing these libraries, I'd be delighted to do so.


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