1 #include <math.h>
2
remquol(long double x,long double y,int * quo)3 long double remquol(long double x, long double y, int *quo)
4 {
5 signed char *cx = (void *)&x, *cy = (void *)&y;
6 /* By ensuring that addresses of x and y cannot be discarded,
7 * this empty asm guides GCC into representing extraction of
8 * their sign bits as memory loads rather than making x and y
9 * not-address-taken internally and using bitfield operations,
10 * which in the end wouldn't work out, as extraction from FPU
11 * registers needs to go through memory anyway. This way GCC
12 * should manage to use incoming stack slots without spills. */
13 __asm__ ("" :: "X"(cx), "X"(cy));
14
15 long double t = x;
16 unsigned fpsr;
17 do __asm__ ("fprem1; fnstsw %%ax" : "+t"(t), "=a"(fpsr) : "u"(y));
18 while (fpsr & 0x400);
19 /* C0, C1, C3 flags in x87 status word carry low bits of quotient:
20 * 15 14 13 12 11 10 9 8
21 * . C3 . . . C2 C1 C0
22 * . b1 . . . 0 b0 b2 */
23 unsigned char i = fpsr >> 8;
24 i = i>>4 | i<<4;
25 /* i[5:2] is now {b0 b2 ? b1}. Retrieve {0 b2 b1 b0} via
26 * in-register table lookup. */
27 unsigned qbits = 0x7575313164642020 >> (i & 60);
28 qbits &= 7;
29
30 *quo = (cx[9]^cy[9]) < 0 ? -qbits : qbits;
31 return t;
32 }
33