CHAPTER 17. FLOATING-POINT UNIT CHAPTER 17. FLOATING-POINT UNIT
Thefloattype requires the same number of bits as theinttype in 32-bit environments, but the number representation is
completely different.
17.5 Simple example
Let’s consider this simple example:
#include <stdio.h>
double f (double a, double b)
{
return a/3.14 + b*4.1;
};
int main()
{
printf ("%f\n", f(1.2, 3.4));
};
17.5.1 x86
MSVC
Compile it in MSVC 2010:
Listing 17.1: MSVC 2010:f()CONST SEGMENT
real@4010666666666666 DQ 04010666666666666r ; 4.1
CONST ENDS
CONST SEGMENT
real@40091eb851eb851f DQ 040091eb851eb851fr ; 3.14
CONST ENDS
_TEXT SEGMENT
_a$ = 8 ; size = 8
_b$ = 16 ; size = 8
_f PROC
push ebp
mov ebp, esp
fld QWORD PTR _a$[ebp]
; current stack state: ST(0) = _a
fdiv QWORD PTR __real@40091eb851eb851f; current stack state: ST(0) = result of _a divided by 3.14
fld QWORD PTR _b$[ebp]; current stack state: ST(0) = _b; ST(1) = result of _a divided by 3.14
fmul QWORD PTR __real@4010666666666666; current stack state:
; ST(0) = result of _b * 4.1;
; ST(1) = result of _a divided by 3.14
faddp ST(1), ST(0); current stack state: ST(0) = result of addition
pop ebp
ret 0
_f ENDP