[9fans] kw floating point emulation problem?

[erik quanstrom <quanstro@quanstro.net>]

gs when compiled on arm for arm doesn't work.
gs when compiled on 386 for arm does work.
i boiled down the problem case to this wierd define
from /sys/src/cmd/gs/src/ztype.c

; cat p2.c
#include <u.h>
#include <libc.h>

#define ALT_MIN_LONG (-1L << (sizeof(long) * 8L - 1))

void
main(void)
{
	print("%lx\n", ALT_MIN_LONG);
	print("%lx\n", 0x80000000L);
	print("%g\n", ALT_MIN_LONG*1.);
	print("%g\n", 0x80000000UL*1.);
	exits("");
}
; cpu -c '5c -FVTw p2.c && 5l p2.5' && 5.out	# cpu is a 386
-80000000
-80000000
-2.147484e+09
2.147484e+09
; 5c -FVTw p2.c && 5l p2.5 && 5.out
-80000000
-80000000
6.442451e+09
-2.147484e+09

a little debugging in scon.c yields:
CAST [l->vconst 2147483648] -> n->fconst 6.442451e+09

for /sys/src/cmd/cc/scon.c:51,59
	case OCAST:
		if(et == TVOID)
			return;
		et = l->type->etype;
		if(isf) {
			if(typefd[et])
>>				d = l->fconst;
			else
				d = l->vconst;


- erik