; ifflt_64.asm  code ifflt_64.c for nasm 
; /* ifflt_64.c an 'if' statement that will be coded for nasm */
; #include <stdio.h>
; int main()
; {
;   double a=1.0;
;   double b=2.0;
;   double c=3.0;
;   printf("a=%f  b=%f  c=%f \n",a,b,c) 
;   if(a<b)
;     printf("true a < b \n");
;   end if
;   if(a<b)
;     printf("true a < b \n");
;   else
;     printf("wrong on a < b \n");
;   if(b>c)
;     printf("wrong on b > c \n");
;   else
;     printf("false b > c \n");
;   return 0;
;}
; result of executing both "C" and assembly is:
; true a < b
; false b > c

;; to make code like "C"
;;   do opposite compare, if this true jump to false
;;   do code for true
;;   jump to exit
;;   false label:
;;   do code for false, the else part
;;   exit label:
;;
;; You may to the compare, if true jump to code for true
;; do code for false, jump to exit
	
	
	global	main		; define for linker
        extern	printf		; tell linker we need this C function
        section .data		; Data section, initialized variables
a:	dq 1.0  		; "C" double
b:	dq 2.0
c:	dq 3.0
fmtabc:	db "a=%f  b=%f  c=%f", 10, 0
fmtlt:  db "true a < b ",10,0
fmtgt:  db "true a > b ",10,0
fmtle:  db "true a <= b ",10,0
fmtge:  db "true a >= b ",10,0
fmtteq: db "true a == a ",10,0
fmttne: db "true a != b ",10,0
fmt2:   db "wrong on a < b ",10,0
fmt3:   db "wrong on b > c ",10,0
fmt4:   db "false b > c ",10,0

	section .text
main:	push	rbp		; set up stack
        mov	rdi,fmtabc
	movq	xmm0,qword[a]
	movq	xmm1,qword[b]
	movq	xmm2,qword[c]
	mov 	rax,3 		; three doubles
	call 	printf

	fld	qword [b]	; b into st0
	fld	qword [a]	; a into st0, pushes b into st1
	fcompp			; compare and pop both
	jl	falselt		; choose jump to false part
	; a < b sign is set
        mov	rdi, fmtlt	; printf("true a < b \n");
	mov	rax, 0
        call    printf	
        jmp	exitlt		; jump over false part
falselt:			;  a < b is false 
        mov	rdi, fmt2	; printf("wrong on a < b \n");
	mov	rax, 0
        call    printf
exitlt:				; finished 'if lt' statement

	fld	qword [c]	; c into st0
	fld	qword [b]	; b into st0, pushes c into st1
	fcompp			; compare and pop both
	jg	falsegt		; choose jump to false part
	; b > c sign is not set
        mov	rdi, fmt3	; printf("wrong on b > c \n");
        mov	rax, 0
        call    printf	
        jmp	exitgt		; jump over false part
falsegt:			;  b > c is false 
        mov	rdi, fmt4	; printf("false b > c \n");
	mov	rax, 0
        call    printf
exitgt:				; finished 'if' statement

	pop	rbp		; restore stack
	mov	rax,0		; normal, no error, return value
	ret			; return 0;