From:

Dom Jackson <nospam@mci2000.com>

Newsgroups:

comp.lang.c++,comp.lang.c

Date:

Sat, 23 Jun 2007 19:22:25 +0100

Message-ID:

<fsnq731dpl53npvjjqbb9njt4gdnih3eie@4ax.com>

compiler, -UINT32_MAX = 1, and -UINT64_MAX is also 1 (test code

below).

From the C99 LRM, p79:

"The result of the unary - operator is the negative of its (promoted)

operand. The integer promotions are performed on the operand, and the

result has the promoted type."

As far as I can make out from p43, uint32_t and uint64_t are unchanged

by the integer promotions. So how do you take the negative of an

unsigned operand, and how can the compiler get the result '1' without

using a temporary of a higher precision? Any thoughts?

Thanks -

Dom

--------------------------------------------------------------

[the code below is C++ to simplify data output, and produces this

result]:

i is ffffffff; j is 1; k is 1; l is ffffffffffffffff; -l is 1; m is 1

--------------------------------------------------------------

#define __STDC_LIMIT_MACROS

#include <stdint.h>

#include <iostream>

#include <iomanip>

int main() {

uint32_t i = UINT32_MAX;

int64_t j;

uint64_t k;

uint64_t l = UINT64_MAX;

uint64_t m = -UINT64_MAX;

j = -i;

k = -i;

std::cout << std::hex << std::setfill('0')

<< "i is " << i

<< "; j is " << j

<< "; k is " << k

<< "; l is " << l

<< "; -l is " << -l

<< "; m is " << m

<< std::endl;

return 0;

}

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