Path: chuka.playstation.co.uk!news
From: john.rees@dial.pipex.com
Newsgroups: scee.yaroze.programming.gnu_compiler
Subject: long long ints for improved accuracy
Date: Mon, 15 Dec 1997 13:19:54 GMT
Organization: PlayStation Net Yaroze (SCEE)
Lines: 54
Message-ID: <673auk$9k35@chuka.playstation.co.uk>
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I am trying to use long long ints to hold temporary values during
fixed point calculations, but if I use divide and modulus operations
then the linker complains that certain functions are not found.

gcc basic.o  -Xlinker -Map -Xlinker mapfile -Xlinker -Ttext -Xlinker
80100000 -o basic
basic.o: In function `main':
basic.c:11: undefined reference to `__divdi3'
basic.c:11: relocation truncated to fit: JMPADDR __divdi3
basic.c:12: undefined reference to `__moddi3'
basic.c:12: relocation truncated to fit: JMPADDR __moddi3
make.exe: *** [basic] Error 1

It is strange that add, subtract and multiply seem to work, but divide
and modulus are not provided. Even if these would be slow to execute
on a 32 bit machine, it would be VERY useful.


#include <stdio.h>

#define printll(v) printf(#v "=%08x %08x\n", *(((int*)&v)+1),
*(int*)&v )

int main(void)
{
	long long x = 0x123456;
	long long y = 0x100000;
	long long prod = (x-y)*y;
	long long quot = x/y;
	long long rem = x%y;

	printll(x);
	printll(y);
	printll(prod);
	printll(quot);
	printll(rem);

	return 0;
}

With the "quot" and "rem" lines commented out, the output is:

x=00000000 00123456
y=00000000 00100000
prod=00000023 45600000

Thanks to Alex Amsel for a throwaway remark in the More Pointless
Optimisation Tricks thread that made me aware of long longs. 
After struggling with fixed point numbers for far too many hours I
really hope someone can help with this.

john