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vlop_arm.s
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vlop_arm.s
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// Inferno's libkern/vlop-arm.s
// https://bitbucket.org/inferno-os/inferno-os/src/default/libkern/vlop-arm.s
//
// Copyright © 1994-1999 Lucent Technologies Inc. All rights reserved.
// Revisions Copyright © 2000-2007 Vita Nuova Holdings Limited (www.vitanuova.com). All rights reserved.
// Portions Copyright 2009 The Go Authors. All rights reserved.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.
#include "go_asm.h"
#include "go_tls.h"
#include "funcdata.h"
#include "textflag.h"
// func runtime·udiv(n, d uint32) (q, r uint32)
// compiler knowns the register usage of this function
// Reference:
// Sloss, Andrew et. al; ARM System Developer's Guide: Designing and Optimizing System Software
// Morgan Kaufmann; 1 edition (April 8, 2004), ISBN 978-1558608740
#define Rq R0 // input d, output q
#define Rr R1 // input n, output r
#define Rs R2 // three temporary variables
#define RM R3
#define Ra R11
// Be careful: Ra == R11 will be used by the linker for synthesized instructions.
// Note: this function does not have a frame.
TEXT runtime·udiv(SB),NOSPLIT|NOFRAME,$0
MOVBU internal∕cpu·ARM+const_offsetARMHasIDIVA(SB), Ra
CMP $0, Ra
BNE udiv_hardware
CLZ Rq, Rs // find normalizing shift
MOVW.S Rq<<Rs, Ra
MOVW $fast_udiv_tab<>-64(SB), RM
ADD.NE Ra>>25, RM, Ra // index by most significant 7 bits of divisor
MOVBU.NE (Ra), Ra
SUB.S $7, Rs
RSB $0, Rq, RM // M = -q
MOVW.PL Ra<<Rs, Rq
// 1st Newton iteration
MUL.PL RM, Rq, Ra // a = -q*d
BMI udiv_by_large_d
MULAWT Ra, Rq, Rq, Rq // q approx q-(q*q*d>>32)
TEQ RM->1, RM // check for d=0 or d=1
// 2nd Newton iteration
MUL.NE RM, Rq, Ra
MOVW.NE $0, Rs
MULAL.NE Rq, Ra, (Rq,Rs)
BEQ udiv_by_0_or_1
// q now accurate enough for a remainder r, 0<=r<3*d
MULLU Rq, Rr, (Rq,Rs) // q = (r * q) >> 32
ADD RM, Rr, Rr // r = n - d
MULA RM, Rq, Rr, Rr // r = n - (q+1)*d
// since 0 <= n-q*d < 3*d; thus -d <= r < 2*d
CMN RM, Rr // t = r-d
SUB.CS RM, Rr, Rr // if (t<-d || t>=0) r=r+d
ADD.CC $1, Rq
ADD.PL RM<<1, Rr
ADD.PL $2, Rq
RET
// use hardware divider
udiv_hardware:
DIVUHW Rq, Rr, Rs
MUL Rs, Rq, RM
RSB Rr, RM, Rr
MOVW Rs, Rq
RET
udiv_by_large_d:
// at this point we know d>=2^(31-6)=2^25
SUB $4, Ra, Ra
RSB $0, Rs, Rs
MOVW Ra>>Rs, Rq
MULLU Rq, Rr, (Rq,Rs)
MULA RM, Rq, Rr, Rr
// q now accurate enough for a remainder r, 0<=r<4*d
CMN Rr>>1, RM // if(r/2 >= d)
ADD.CS RM<<1, Rr
ADD.CS $2, Rq
CMN Rr, RM
ADD.CS RM, Rr
ADD.CS $1, Rq
RET
udiv_by_0_or_1:
// carry set if d==1, carry clear if d==0
BCC udiv_by_0
MOVW Rr, Rq
MOVW $0, Rr
RET
udiv_by_0:
MOVW $runtime·panicdivide(SB), R11
B (R11)
// var tab [64]byte
// tab[0] = 255; for i := 1; i <= 63; i++ { tab[i] = (1<<14)/(64+i) }
// laid out here as little-endian uint32s
DATA fast_udiv_tab<>+0x00(SB)/4, $0xf4f8fcff
DATA fast_udiv_tab<>+0x04(SB)/4, $0xe6eaedf0
DATA fast_udiv_tab<>+0x08(SB)/4, $0xdadde0e3
DATA fast_udiv_tab<>+0x0c(SB)/4, $0xcfd2d4d7
DATA fast_udiv_tab<>+0x10(SB)/4, $0xc5c7cacc
DATA fast_udiv_tab<>+0x14(SB)/4, $0xbcbec0c3
DATA fast_udiv_tab<>+0x18(SB)/4, $0xb4b6b8ba
DATA fast_udiv_tab<>+0x1c(SB)/4, $0xacaeb0b2
DATA fast_udiv_tab<>+0x20(SB)/4, $0xa5a7a8aa
DATA fast_udiv_tab<>+0x24(SB)/4, $0x9fa0a2a3
DATA fast_udiv_tab<>+0x28(SB)/4, $0x999a9c9d
DATA fast_udiv_tab<>+0x2c(SB)/4, $0x93949697
DATA fast_udiv_tab<>+0x30(SB)/4, $0x8e8f9092
DATA fast_udiv_tab<>+0x34(SB)/4, $0x898a8c8d
DATA fast_udiv_tab<>+0x38(SB)/4, $0x85868788
DATA fast_udiv_tab<>+0x3c(SB)/4, $0x81828384
GLOBL fast_udiv_tab<>(SB), RODATA, $64
// The linker will pass numerator in R8
#define Rn R8
// The linker expects the result in RTMP
#define RTMP R11
TEXT runtime·_divu(SB), NOSPLIT, $16-0
// It's not strictly true that there are no local pointers.
// It could be that the saved registers Rq, Rr, Rs, and Rm
// contain pointers. However, the only way this can matter
// is if the stack grows (which it can't, udiv is nosplit)
// or if a fault happens and more frames are added to
// the stack due to deferred functions.
// In the latter case, the stack can grow arbitrarily,
// and garbage collection can happen, and those
// operations care about pointers, but in that case
// the calling frame is dead, and so are the saved
// registers. So we can claim there are no pointers here.
NO_LOCAL_POINTERS
MOVW Rq, 4(R13)
MOVW Rr, 8(R13)
MOVW Rs, 12(R13)
MOVW RM, 16(R13)
MOVW Rn, Rr /* numerator */
MOVW g_m(g), Rq
MOVW m_divmod(Rq), Rq /* denominator */
BL runtime·udiv(SB)
MOVW Rq, RTMP
MOVW 4(R13), Rq
MOVW 8(R13), Rr
MOVW 12(R13), Rs
MOVW 16(R13), RM
RET
TEXT runtime·_modu(SB), NOSPLIT, $16-0
NO_LOCAL_POINTERS
MOVW Rq, 4(R13)
MOVW Rr, 8(R13)
MOVW Rs, 12(R13)
MOVW RM, 16(R13)
MOVW Rn, Rr /* numerator */
MOVW g_m(g), Rq
MOVW m_divmod(Rq), Rq /* denominator */
BL runtime·udiv(SB)
MOVW Rr, RTMP
MOVW 4(R13), Rq
MOVW 8(R13), Rr
MOVW 12(R13), Rs
MOVW 16(R13), RM
RET
TEXT runtime·_div(SB),NOSPLIT,$16-0
NO_LOCAL_POINTERS
MOVW Rq, 4(R13)
MOVW Rr, 8(R13)
MOVW Rs, 12(R13)
MOVW RM, 16(R13)
MOVW Rn, Rr /* numerator */
MOVW g_m(g), Rq
MOVW m_divmod(Rq), Rq /* denominator */
CMP $0, Rr
BGE d1
RSB $0, Rr, Rr
CMP $0, Rq
BGE d2
RSB $0, Rq, Rq
d0:
BL runtime·udiv(SB) /* none/both neg */
MOVW Rq, RTMP
B out1
d1:
CMP $0, Rq
BGE d0
RSB $0, Rq, Rq
d2:
BL runtime·udiv(SB) /* one neg */
RSB $0, Rq, RTMP
out1:
MOVW 4(R13), Rq
MOVW 8(R13), Rr
MOVW 12(R13), Rs
MOVW 16(R13), RM
RET
TEXT runtime·_mod(SB),NOSPLIT,$16-0
NO_LOCAL_POINTERS
MOVW Rq, 4(R13)
MOVW Rr, 8(R13)
MOVW Rs, 12(R13)
MOVW RM, 16(R13)
MOVW Rn, Rr /* numerator */
MOVW g_m(g), Rq
MOVW m_divmod(Rq), Rq /* denominator */
CMP $0, Rq
RSB.LT $0, Rq, Rq
CMP $0, Rr
BGE m1
RSB $0, Rr, Rr
BL runtime·udiv(SB) /* neg numerator */
RSB $0, Rr, RTMP
B out
m1:
BL runtime·udiv(SB) /* pos numerator */
MOVW Rr, RTMP
out:
MOVW 4(R13), Rq
MOVW 8(R13), Rr
MOVW 12(R13), Rs
MOVW 16(R13), RM
RET
// _mul64by32 and _div64by32 not implemented on arm
TEXT runtime·_mul64by32(SB), NOSPLIT, $0
MOVW $0, R0
MOVW (R0), R1 // crash
TEXT runtime·_div64by32(SB), NOSPLIT, $0
MOVW $0, R0
MOVW (R0), R1 // crash