Example 2-23 Algorithm To Avoid Changing The Rounding Mode - Intel ARCHITECTURE IA-32 Reference Manual

IA-32 Intel® Architecture Optimization

Example 2-23 Algorithm to Avoid Changing the Rounding Mode

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