arch/arm/lib/uldivmod.S

/* SPDX-License-Identifier: GPL-2.0 */
/*
 * Copyright 2010, Google Inc.
 *
 * Brought in from coreboot uldivmod.S
 */

#include <linux/linkage.h>
#include <asm/assembler.h>

/*
 * A, Q = r0 + (r1 << 32)
 * B, R = r2 + (r3 << 32)
 * A / B = Q ... R
 */

A_0	.req	r0
A_1	.req	r1
B_0	.req	r2
B_1	.req	r3
C_0	.req	r4
C_1	.req	r5
D_0	.req	r6
D_1	.req	r7

Q_0	.req	r0
Q_1	.req	r1
R_0	.req	r2
R_1	.req	r3

THUMB(
TMP	.req	r8
)

.pushsection .text.__aeabi_uldivmod, "ax"
ENTRY(__aeabi_uldivmod)

	stmfd	sp!, {r4, r5, r6, r7, THUMB(TMP,) lr}
	@ Test if B == 0
	orrs	ip, B_0, B_1		@ Z set -> B == 0
	beq	L_div_by_0
	@ Test if B is power of 2: (B & (B - 1)) == 0
	subs	C_0, B_0, #1
	sbc	C_1, B_1, #0
	tst	C_0, B_0
	tsteq	B_1, C_1
	beq	L_pow2
	@ Test if A_1 == B_1 == 0
	orrs	ip, A_1, B_1
	beq	L_div_32_32

L_div_64_64:
/* CLZ only exists in ARM architecture version 5 and above. */
#ifdef HAVE_CLZ
	mov	C_0, #1
	mov	C_1, #0
	@ D_0 = clz A
	teq	A_1, #0
	clz	D_0, A_1
	clzeq	ip, A_0
	addeq	D_0, D_0, ip
	@ D_1 = clz B
	teq	B_1, #0
	clz	D_1, B_1
	clzeq	ip, B_0
	addeq	D_1, D_1, ip
	@ if clz B - clz A > 0
	subs	D_0, D_1, D_0
	bls	L_done_shift
	@ B <<= (clz B - clz A)
	subs	D_1, D_0, #32
	rsb	ip, D_0, #32
	movmi	B_1, B_1, lsl D_0
ARM(	orrmi	B_1, B_1, B_0, lsr ip	)
THUMB(	lsrmi	TMP, B_0, ip		)
THUMB(	orrmi	B_1, B_1, TMP		)
	movpl	B_1, B_0, lsl D_1
	mov	B_0, B_0, lsl D_0
	@ C = 1 << (clz B - clz A)
	movmi	C_1, C_1, lsl D_0
ARM(	orrmi	C_1, C_1, C_0, lsr ip	)
THUMB(	lsrmi	TMP, C_0, ip		)
THUMB(	orrmi	C_1, C_1, TMP		)
	movpl	C_1, C_0, lsl D_1
	mov	C_0, C_0, lsl D_0
L_done_shift:
	mov	D_0, #0
	mov	D_1, #0
	@ C: current bit; D: result
#else
	@ C: current bit; D: result
	mov	C_0, #1
	mov	C_1, #0
	mov	D_0, #0
	mov	D_1, #0
L_lsl_4:
	cmp	B_1, #0x10000000
	cmpcc	B_1, A_1
	cmpeq	B_0, A_0
	bcs	L_lsl_1
	@ B <<= 4
	mov	B_1, B_1, lsl #4
	orr	B_1, B_1, B_0, lsr #28
	mov	B_0, B_0, lsl #4
	@ C <<= 4
	mov	C_1, C_1, lsl #4
	orr	C_1, C_1, C_0, lsr #28
	mov	C_0, C_0, lsl #4
	b	L_lsl_4
L_lsl_1:
	cmp	B_1, #0x80000000
	cmpcc	B_1, A_1
	cmpeq	B_0, A_0
	bcs	L_subtract
	@ B <<= 1
	mov	B_1, B_1, lsl #1
	orr	B_1, B_1, B_0, lsr #31
	mov	B_0, B_0, lsl #1
	@ C <<= 1
	mov	C_1, C_1, lsl #1
	orr	C_1, C_1, C_0, lsr #31
	mov	C_0, C_0, lsl #1
	b	L_lsl_1
#endif
L_subtract:
	@ if A >= B
	cmp	A_1, B_1
	cmpeq	A_0, B_0
	bcc	L_update
	@ A -= B
	subs	A_0, A_0, B_0
	sbc	A_1, A_1, B_1
	@ D |= C
	orr	D_0, D_0, C_0
	orr	D_1, D_1, C_1
L_update:
	@ if A == 0: break
	orrs	ip, A_1, A_0
	beq	L_exit
	@ C >>= 1
	movs	C_1, C_1, lsr #1
	movs	C_0, C_0, rrx
	@ if C == 0: break
	orrs	ip, C_1, C_0
	beq	L_exit
	@ B >>= 1
	movs	B_1, B_1, lsr #1
	mov	B_0, B_0, rrx
	b	L_subtract
L_exit:
	@ Note: A, B & Q, R are aliases
	mov	R_0, A_0
	mov	R_1, A_1
	mov	Q_0, D_0
	mov	Q_1, D_1
	ldmfd	sp!, {r4, r5, r6, r7, THUMB(TMP,) pc}

L_div_32_32:
	@ Note:	A_0 &	r0 are aliases
	@	Q_1	r1
	mov	r1, B_0
	bl	__aeabi_uidivmod
	mov	R_0, r1
	mov	R_1, #0
	mov	Q_1, #0
	ldmfd	sp!, {r4, r5, r6, r7, THUMB(TMP,) pc}

L_pow2:
#ifdef HAVE_CLZ
	@ Note: A, B and Q, R are aliases
	@ R = A & (B - 1)
	and	C_0, A_0, C_0
	and	C_1, A_1, C_1
	@ Q = A >> log2(B)
	@ Note: B must not be 0 here!
	clz	D_0, B_0
	add	D_1, D_0, #1
	rsbs	D_0, D_0, #31
	bpl	L_1
	clz	D_0, B_1
	rsb	D_0, D_0, #31
	mov	A_0, A_1, lsr D_0
	add	D_0, D_0, #32
L_1:
	movpl	A_0, A_0, lsr D_0
ARM(	orrpl	A_0, A_0, A_1, lsl D_1	)
THUMB(	lslpl	TMP, A_1, D_1		)
THUMB(	orrpl	A_0, A_0, TMP		)
	mov	A_1, A_1, lsr D_0
	@ Mov back C to R
	mov	R_0, C_0
	mov	R_1, C_1
	ldmfd	sp!, {r4, r5, r6, r7, THUMB(TMP,) pc}
#else
	@ Note: A, B and Q, R are aliases
	@ R = A & (B - 1)
	and	C_0, A_0, C_0
	and	C_1, A_1, C_1
	@ Q = A >> log2(B)
	@ Note: B must not be 0 here!
	@ Count the leading zeroes in B.
	mov	D_0, #0
	orrs	B_0, B_0, B_0
	@ If B is greater than 1 << 31, divide A and B by 1 << 32.
	moveq	A_0, A_1
	moveq	A_1, #0
	moveq	B_0, B_1
	@ Count the remaining leading zeroes in B.
	movs	B_1, B_0, lsl #16
	addeq	D_0, #16
	moveq	B_0, B_0, lsr #16
	tst	B_0, #0xff
	addeq	D_0, #8
	moveq	B_0, B_0, lsr #8
	tst	B_0, #0xf
	addeq	D_0, #4
	moveq	B_0, B_0, lsr #4
	tst	B_0, #0x3
	addeq	D_0, #2
	moveq	B_0, B_0, lsr #2
	tst	B_0, #0x1
	addeq	D_0, #1
	@ Shift A to the right by the appropriate amount.
	rsb	D_1, D_0, #32
	mov	Q_0, A_0, lsr D_0
 ARM(   orr     Q_0, Q_0, A_1, lsl D_1	)
 THUMB(	lsl	A_1, D_1		)
 THUMB(	orr	Q_0, A_1		)
	mov	Q_1, A_1, lsr D_0
	@ Move C to R
	mov	R_0, C_0
	mov	R_1, C_1
	ldmfd	sp!, {r4, r5, r6, r7, THUMB(TMP,) pc}
#endif

L_div_by_0:
	bl	__div0
	@ As wrong as it could be
	mov	Q_0, #0
	mov	Q_1, #0
	mov	R_0, #0
	mov	R_1, #0
	ldmfd	sp!, {r4, r5, r6, r7, THUMB(TMP,) pc}
ENDPROC(__aeabi_uldivmod)
.popsection