diff options
Diffstat (limited to 'libc/i386fp/fcomp.x')
| -rw-r--r-- | libc/i386fp/fcomp.x | 89 |
1 files changed, 89 insertions, 0 deletions
diff --git a/libc/i386fp/fcomp.x b/libc/i386fp/fcomp.x new file mode 100644 index 0000000..71148ab --- /dev/null +++ b/libc/i386fp/fcomp.x @@ -0,0 +1,89 @@ +! bcc 386 floating point routines (version 2) -- Fcomp, Fcompd, Fcompf +! authors: Timothy Murphy (tim@maths.tcd.ie), Bruce Evans + +#include "fplib.h" + + .extern Fpushf + +! Pop 2 doubles from stack and compare them, return result in flags so +! normal signed branches work (unlike 80x87 which returns the result in +! the zero and carry flags). + + .globl Fcomp + .align ALIGNMENT +Fcomp: + pop ecx ! get return address + pop eax ! xl + pop edx ! xu + push ecx ! put back ret address - pop 2nd double later + +! All this popping is bad on 486's since plain mov takes 1+ cycle and pop +! takes 4 cycles. But this code is designed for 386's where popping is +! nominally the same speed and saves code space and so maybe instruction +! fetch time as well as the instruction to adjust the stack (ret #n takes +! no longer than plain ret but inhibits gotos). + + mov ebx,PC_SIZE+D_LOW[esp] ! yl + mov ecx,PC_SIZE+D_HIGH[esp] ! yu + jmp compare + +! Pop double from stack and compare with double at [ebx] + + .globl Fcompd + .align ALIGNMENT +Fcompd: + mov eax,PC_SIZE+D_LOW[esp] ! xl + mov edx,PC_SIZE+D_HIGH[esp] ! xu + mov ecx,D_HIGH[ebx] ! yu + mov ebx,D_LOW[ebx] ! yl + +compare: + test edx,#D_SIGN_MASK ! is x >= 0? + jz cmp0 ! yes; just compare x and y + test ecx,#D_SIGN_MASK ! no; but is y >= 0? + jz cmp0 ! yes; just compare x and y + + xchg edx,ecx ! x, y < 0, so ... + xchg eax,ebx ! ... swap x and y ... + xor edx,#D_SIGN_MASK ! ... and toggle signs + xor ecx,#D_SIGN_MASK + +cmp0: + cmp edx,ecx ! compare upper dwords + jnz checkneg0 ! if upper dwords differ, job is almost done + mov edx,eax ! upper dwords equal, so ... + mov ecx,ebx ! ... must make unsigned comparison of lower dwords + shr edx,#1 ! shift past sign + shr ecx,#1 + cmp edx,ecx ! compare top 31 bits of lower dwords + jnz return ! if these differ, job is done + and eax,#1 ! compare lowest bits + and ebx,#1 + cmp eax,ebx + +return: + ret #D_SIZE ! return, popping 1 double from stack + +checkneg0: + test edx,#D_EXP_MASK | D_FRAC_MASK ! check to catch unusual case ... + jnz recheck + test eax,eax + jnz recheck + test ecx,#D_EXP_MASK | D_FRAC_MASK + jnz recheck + test ebx,ebx + jz return ! ... both are (+-) zero, return 'z' + +recheck: + cmp edx,ecx ! the upper words were really different + ret #D_SIZE + + .globl Fcompf + .align ALIGNMENT +Fcompf: + call Fpushf + pop ebx ! yl + pop ecx ! yu + mov eax,PC_SIZE+D_LOW[esp] ! xl + mov edx,PC_SIZE+D_HIGH[esp] ! xu + jmp compare |