c+asm

gistfile1.txt

///////////////////////////
//main.c
///////////////////////////

extern void delay(int milli);
extern long long mult(long a, long b);

#define MS_DELAY 1000

int main(void)
{

  long long res;
  long a = 4;
  long b = 1000000000;
  res = mult(a,b);
  
  delay(MS_DELAY);
  
  for(;;);

}


///////////////////////////
//libasm.s
///////////////////////////

.equ	  SYS_REGS,   0x400FE000
.equ	  PORTF_BASE, 0x40025000
.syntax unified
.thumb
# -------------------------------------
# void delay(int n)
# -------------------------------------
.global delay
delay: 
	movw  r1, #2664
delay_l0:
	subs r1, r1, #1
	bne	delay_l0
	subs r0, r0, #1
	bne  delay
	mov pc, lr
  
# -------------------------------------
# long long mult(long a, long b)
# -------------------------------------
.global mult
mult:
	sub  	sp, #4
	str		r4, [sp, #0]
	movs  	r4, #1
	mov		r2, r1
	movs  	r1, #0
	movs  	r3, #32
mult_l0:
	lsrs  	r0, r0, #1
	it    	cs
	addscs 	r1, r1, r2
	rrxs  	r1, r1
	it    	cs
	addcs 	r0, r0, r4, LSL #31
	subs  	r3, r3, #1
	bne  	mult_l0
	ldr 	r4, [sp, #0]
	add  	sp, #4
	mov  	pc, lr
  
  # -------------------------------------
# int invert_bits(int byte)
# 
# r6	   - 0
# r5       - 4
# r4       - 8
# lr	   - 12
# char     - 16
# ret_val  - 20
# -------------------------------------
.global invert_bits
invert_bits:
	push {lr}
	push {r4}
	push {r5}
	push {r6}
	mov  r4, #32
	mov  r5, #0
	ldr  r6, [sp, #16]
ib0:lsl  r5, #1
	cmp  r6, #0
	bmi  ib1
	add  r5, #1
ib1:lsl  r6, #1
	subs r4, #1
	bne	 ib0
	str  r5, [sp, #20]
	pop  {r6}
	pop  {r5}
	pop  {r4}
	pop  {pc}