Intel ARCHITECTURE IA-32 - Manual (Page 138)

IA-32 Intel® Architecture Optimization
2-66
Example 2-23 Algorithm to Avoid Changing the Rounding Mode
_fto132proc
lea ecx,[esp-8]
sub esp,16 ; allocate frame
and ecx,-8 ; align pointer on boundary of 8
fld st(0) ; duplicate FPU stack top
fistp qword ptr[ecx]
fild qword ptr[ecx]
mov edx,[ecx+4]; high dword of integer
mov eax,[ecx] ; low dword of integer
test eax,eax
je integer_QnaN_or_zero
arg_is_not_integer_QnaN:
fsubp st(1),st ; TOS=d-round(d),
; { st(1)=st(1)-st & pop ST}
test edx,edx ; what’s sign of integer
jns positive ; number is negative
fstp dword ptr[ecx]; result of subtraction
mov ecx,[ecx] ; dword of diff(single-
; precision)
add esp,16
xor ecx,80000000h
add ecx,7fffffffh ; if diff<0 then decrement
; integer
adc eax,0 ; inc eax (add CARRY flag)
ret
positive:
continued