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| /*
| * linux/arch/arm/lib/div64.S
| *
| * Optimized computation of 64-bit dividend / 32-bit divisor
| *
| * Author: Nicolas Pitre
| * Created: Oct 5, 2003
| * Copyright: Monta Vista Software, Inc.
| *
| * SPDX-License-Identifier: GPL-2.0
| */
|
| #include <linux/linkage.h>
| #include <asm/assembler.h>
| #ifdef __UBOOT__
| #define UNWIND(x...)
| #endif
|
| #ifdef __ARMEB__
| #define xh r0
| #define xl r1
| #define yh r2
| #define yl r3
| #else
| #define xl r0
| #define xh r1
| #define yl r2
| #define yh r3
| #endif
|
| /*
| * __do_div64: perform a division with 64-bit dividend and 32-bit divisor.
| *
| * Note: Calling convention is totally non standard for optimal code.
| * This is meant to be used by do_div() from include/asm/div64.h only.
| *
| * Input parameters:
| * xh-xl = dividend (clobbered)
| * r4 = divisor (preserved)
| *
| * Output values:
| * yh-yl = result
| * xh = remainder
| *
| * Clobbered regs: xl, ip
| */
|
| .pushsection .text.__do_div64, "ax"
| ENTRY(__do_div64)
| UNWIND(.fnstart)
|
| @ Test for easy paths first.
| subs ip, r4, #1
| bls 9f @ divisor is 0 or 1
| tst ip, r4
| beq 8f @ divisor is power of 2
|
| @ See if we need to handle upper 32-bit result.
| cmp xh, r4
| mov yh, #0
| blo 3f
|
| @ Align divisor with upper part of dividend.
| @ The aligned divisor is stored in yl preserving the original.
| @ The bit position is stored in ip.
|
| #if __LINUX_ARM_ARCH__ >= 5
|
| clz yl, r4
| clz ip, xh
| sub yl, yl, ip
| mov ip, #1
| mov ip, ip, lsl yl
| mov yl, r4, lsl yl
|
| #else
|
| mov yl, r4
| mov ip, #1
| 1: cmp yl, #0x80000000
| cmpcc yl, xh
| movcc yl, yl, lsl #1
| movcc ip, ip, lsl #1
| bcc 1b
|
| #endif
|
| @ The division loop for needed upper bit positions.
| @ Break out early if dividend reaches 0.
| 2: cmp xh, yl
| orrcs yh, yh, ip
| subscs xh, xh, yl
| movsne ip, ip, lsr #1
| mov yl, yl, lsr #1
| bne 2b
|
| @ See if we need to handle lower 32-bit result.
| 3: cmp xh, #0
| mov yl, #0
| cmpeq xl, r4
| movlo xh, xl
| retlo lr
|
| @ The division loop for lower bit positions.
| @ Here we shift remainer bits leftwards rather than moving the
| @ divisor for comparisons, considering the carry-out bit as well.
| mov ip, #0x80000000
| 4: movs xl, xl, lsl #1
| adcs xh, xh, xh
| beq 6f
| cmpcc xh, r4
| 5: orrcs yl, yl, ip
| subcs xh, xh, r4
| movs ip, ip, lsr #1
| bne 4b
| ret lr
|
| @ The top part of remainder became zero. If carry is set
| @ (the 33th bit) this is a false positive so resume the loop.
| @ Otherwise, if lower part is also null then we are done.
| 6: bcs 5b
| cmp xl, #0
| reteq lr
|
| @ We still have remainer bits in the low part. Bring them up.
|
| #if __LINUX_ARM_ARCH__ >= 5
|
| clz xh, xl @ we know xh is zero here so...
| add xh, xh, #1
| mov xl, xl, lsl xh
| mov ip, ip, lsr xh
|
| #else
|
| 7: movs xl, xl, lsl #1
| mov ip, ip, lsr #1
| bcc 7b
|
| #endif
|
| @ Current remainder is now 1. It is worthless to compare with
| @ divisor at this point since divisor can not be smaller than 3 here.
| @ If possible, branch for another shift in the division loop.
| @ If no bit position left then we are done.
| movs ip, ip, lsr #1
| mov xh, #1
| bne 4b
| ret lr
|
| 8: @ Division by a power of 2: determine what that divisor order is
| @ then simply shift values around
|
| #if __LINUX_ARM_ARCH__ >= 5
|
| clz ip, r4
| rsb ip, ip, #31
|
| #else
|
| mov yl, r4
| cmp r4, #(1 << 16)
| mov ip, #0
| movhs yl, yl, lsr #16
| movhs ip, #16
|
| cmp yl, #(1 << 8)
| movhs yl, yl, lsr #8
| addhs ip, ip, #8
|
| cmp yl, #(1 << 4)
| movhs yl, yl, lsr #4
| addhs ip, ip, #4
|
| cmp yl, #(1 << 2)
| addhi ip, ip, #3
| addls ip, ip, yl, lsr #1
|
| #endif
|
| mov yh, xh, lsr ip
| mov yl, xl, lsr ip
| rsb ip, ip, #32
| ARM( orr yl, yl, xh, lsl ip )
| THUMB( lsl xh, xh, ip )
| THUMB( orr yl, yl, xh )
| mov xh, xl, lsl ip
| mov xh, xh, lsr ip
| ret lr
|
| @ eq -> division by 1: obvious enough...
| 9: moveq yl, xl
| moveq yh, xh
| moveq xh, #0
| reteq lr
| UNWIND(.fnend)
|
| UNWIND(.fnstart)
| UNWIND(.pad #4)
| UNWIND(.save {lr})
| Ldiv0_64:
| @ Division by 0:
| str lr, [sp, #-8]!
| bl __div0
|
| @ as wrong as it could be...
| mov yl, #0
| mov yh, #0
| mov xh, #0
| ldr pc, [sp], #8
|
| UNWIND(.fnend)
| ENDPROC(__do_div64)
| .popsection
|
|
