Assembly x64 Intro - Floating Point Operate

; fltarith_64.asm   show some simple C code and corresponding nasm code
;                   the nasm code is one sample, not unique
;
; compile  nasm -f elf64 -l fltarith_64.lst  fltarith_64.asm
; link     gcc -m64 -o fltarith_64  fltarith_64.o
; run      ./fltarith_64 > fltarith_64.out
;
; the output from running fltarith and fltarithc is: 
; c=5.0, a=3.000000e+00, b=4.000000e+00, c=5.000000e+00
; c=a+b, a=3.000000e+00, b=4.000000e+00, c=7.000000e+00
; c=a-b, a=3.000000e+00, b=4.000000e+00, c=-1.000000e+00
; c=a*b, a=3.000000e+00, b=4.000000e+00, c=1.200000e+01
; c=c/a, a=3.000000e+00, b=4.000000e+00, c=4.000000e+00
; a=i  , a=8.000000e+00, b=1.600000e+01, c=1.600000e+01
; a<=b , a=8.000000e+00, b=1.600000e+01, c=1.600000e+01
; b==c , a=8.000000e+00, b=1.600000e+01, c=1.600000e+01
;The file  fltarith.c  is:
;  #include <stdio.h>
;  int main()
;  {
;    double a=3.0, b=4.0, c;
;    long int i=8;
;
;    c=5.0;
;    printf("%s, a=%e, b=%e, c=%e\n","c=5.0", a, b, c);
;    c=a+b;
;    printf("%s, a=%e, b=%e, c=%e\n","c=a+b", a, b, c);
;    c=a-b;
;    printf("%s, a=%e, b=%e, c=%e\n","c=a-b", a, b, c);
;    c=a*b;
;    printf("%s, a=%e, b=%e, c=%e\n","c=a*b", a, b, c);
;    c=c/a;
;    printf("%s, a=%e, b=%e, c=%e\n","c=c/a", a, b, c);
;    a=i;
;    b=a+i;
;    i=b;
;    c=i;
;    printf("%s, a=%e, b=%e, c=%e\n","c=c/a", a, b, c);
;    if(ab  ", a, b, c);
;    if(b==c)printf("%s, a=%e, b=%e, c=%e\n","b==c ", a, b, c);
;    else    printf("%s, a=%e, b=%e, c=%e\n","b!=c ", a, b, c);
;    return 0;
; }

        extern printf  ; the C function to be called

%macro pabc 1   ; a "simple" print macro
 section .data
.str db %1,0  ; %1 is macro call first actual parameter
 section .text
    ; push onto stack backwards
        mov rdi, fmt ; address of format string
 mov rsi, .str ; string passed to macro
 movq xmm0, qword [a] ; first floating point in fmt
 movq xmm1, qword [b] ; second floating point
 movq xmm2, qword [c] ; third floating point
 mov rax, 3  ; 3 floating point arguments to printf
        call    printf          ; Call C function
%endmacro
 
 section .data    ; preset constants, writable
a: dq 3.0  ; 64-bit variable a initialized to 3.0
b: dq 4.0  ; 64-bit variable b initializes to 4.0
i: dq 8  ; a 64 bit integer
five: dq 5.0  ; constant 5.0
fmt:    db "%s, a=%e, b=%e, c=%e",10,0 ; format string for printf
 
 section .bss   ; uninitialized space
c: resq 1  ; reserve a 64-bit word

 section .text  ; instructions, code segment
 global main  ; for gcc standard linking
main:    ; label

 push rbp  ; set up stack
lit5:    ; c=5.0;
 fld qword [five] ; 5.0 constant
 fstp qword [c] ; store into c
 pabc "c=5.0"  ; invoke the print macro
 
addb:    ; c=a+b;
 fld qword [a]  ; load a (pushed on flt pt stack, st0)
 fadd qword [b] ; floating add b (to st0)
 fstp qword [c] ; store into c (pop flt pt stack)
 pabc "c=a+b"  ; invoke the print macro
 
subb:    ; c=a-b;
 fld qword [a]  ; load a (pushed on flt pt stack, st0)
 fsub qword [b] ; floating subtract b (to st0)
 fstp qword [c] ; store into c (pop flt pt stack)
 pabc "c=a-b"  ; invoke the print macro
 
mulb:    ; c=a*b;
 fld qword [a] ; load a (pushed on flt pt stack, st0)
 fmul qword [b] ; floating multiply by b (to st0)
 fstp qword [c] ; store product into c (pop flt pt stack)
 pabc "c=a*b"  ; invoke the print macro
 
diva:    ; c=c/a;
 fld qword [c]  ; load c (pushed on flt pt stack, st0)
 fdiv qword [a] ; floating divide by a (to st0)
 fstp qword [c] ; store quotient into c (pop flt pt stack)
 pabc "c=c/a"  ; invoke the print macro

intflt:    ; a=i;
 fild dword [i] ; load integer as floating point
 fst qword [a] ; store the floating point (no pop)
 fadd st0  ; b=a+i; 'a' as 'i'  already on flt stack
 fst qword [b] ; store sum (no pop) 'b' still on stack
 fistp dword [i] ; i=b; store floating point as integer
 fild dword [i] ; c=i; load again from ram (redundant)
 fstp qword [c]
 pabc "a=i  "  ; invoke the print macro

cmpflt: fld dword [b] ; into st0, then pushed to st1
 fld dword [a] ; in st0
 fcomip st0,st1  ; a compare b, pop a
 jg cmpfl2
 pabc "a<=b "
 jmp cmpfl3
cmpfl2: 
 pabc "a>b  "
cmpfl3:
 fld dword [c] ; should equal [b]
 fcomip  st0,st1
 jne cmpfl4
 pabc "b==c "
 jmp cmpfl5
cmpfl4:
 pabc "b!=c "
cmpfl5:

 pop rbp  ; pop stack
        mov     rax,0           ; exit code, 0=normal
 ret   ; main returns to operating system