Re: [C, C++] fundamental type object representation

[Ian Lance Taylor <ian at airs dot com>]

Gabriel Dos Reis <gdr@integrable-solutions.net> writes:

>   Does GCC support any target where the object representation of a
> fundamental type T (e.g. int, float, double, pointers) whose all bits
> are zero does not hold value (T)0?

Surprisingly, the answer seems to be yes.  For the C4X target, a
single precision floating point zero is apparently represented as
0x80000000 (for double precision there is another 32 zero bits).

That said, it doesn't actually work correctly.  Compiling

float f;
float g = 0.0;
struct s { int i; float f; int j; };
struct s sv = { 1, 0.0, 2 };

gives me

	.file	"foo.c"
	.version	40

	.data
data_sec:
	.global	_g
	.globl	_g
	.bss	_g,1
	.global	_sv
	.data
_sv:
	.word	1
	.word	-2147483648
	.word	2
	.globl	_f
	.bss	_f,1
	.end

In other words, the floating point zero is only generated correctly
when gcc is forced to output the initializer for some other reason.

Given that doesn't work, it is probably reasonably safe to assume gcc
is always going to generate all zero bits for a fundamental types
initialized to zero.

Ian