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