arch/arm/lib/_modsi3.S

#include <linux/linkage.h>

.macro ARM_MOD_BODY dividend, divisor, order, spare

#if __LINUX_ARM_ARCH__ >= 5

	clz	\order, \divisor
	clz	\spare, \dividend
	sub	\order, \order, \spare
	mov	\divisor, \divisor, lsl \order

#else

	mov	\order, #0

	@ Unless the divisor is very big, shift it up in multiples of
	@ four bits, since this is the amount of unwinding in the main
	@ division loop.  Continue shifting until the divisor is
	@ larger than the dividend.
1:	cmp	\divisor, #0x10000000
	cmplo	\divisor, \dividend
	movlo	\divisor, \divisor, lsl #4
	addlo	\order, \order, #4
	blo	1b

	@ For very big divisors, we must shift it a bit at a time, or
	@ we will be in danger of overflowing.
1:	cmp	\divisor, #0x80000000
	cmplo	\divisor, \dividend
	movlo	\divisor, \divisor, lsl #1
	addlo	\order, \order, #1
	blo	1b

#endif

	@ Perform all needed substractions to keep only the reminder.
	@ Do comparisons in batch of 4 first.
	subs	\order, \order, #3		@ yes, 3 is intended here
	blt	2f

1:	cmp	\dividend, \divisor
	subhs	\dividend, \dividend, \divisor
	cmp	\dividend, \divisor,  lsr #1
	subhs	\dividend, \dividend, \divisor, lsr #1
	cmp	\dividend, \divisor,  lsr #2
	subhs	\dividend, \dividend, \divisor, lsr #2
	cmp	\dividend, \divisor,  lsr #3
	subhs	\dividend, \dividend, \divisor, lsr #3
	cmp	\dividend, #1
	mov	\divisor, \divisor, lsr #4
	subges	\order, \order, #4
	bge	1b

	tst	\order, #3
	teqne	\dividend, #0
	beq	5f

	@ Either 1, 2 or 3 comparison/substractions are left.
2:	cmn	\order, #2
	blt	4f
	beq	3f
	cmp	\dividend, \divisor
	subhs	\dividend, \dividend, \divisor
	mov	\divisor,  \divisor,  lsr #1
3:	cmp	\dividend, \divisor
	subhs	\dividend, \dividend, \divisor
	mov	\divisor,  \divisor,  lsr #1
4:	cmp	\dividend, \divisor
	subhs	\dividend, \dividend, \divisor
5:
.endm

	.align	5
ENTRY(__modsi3)
	cmp	r1, #0
	beq	Ldiv0
	rsbmi	r1, r1, #0			@ loops below use unsigned.
	movs	ip, r0				@ preserve sign of dividend
	rsbmi	r0, r0, #0			@ if negative make positive
	subs	r2, r1, #1			@ compare divisor with 1
	cmpne	r0, r1				@ compare dividend with divisor
	moveq	r0, #0
	tsthi	r1, r2				@ see if divisor is power of 2
	andeq	r0, r0, r2
	bls	10f

	ARM_MOD_BODY r0, r1, r2, r3

10:	cmp	ip, #0
	rsbmi	r0, r0, #0
	mov	pc, lr
ENDPROC(__modsi3)

Ldiv0:

	str	lr, [sp, #-4]!
	bl	__div0
	mov	r0, #0			@ About as wrong as it could be.
	ldr	pc, [sp], #4