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vlop_arm.s
// Inferno's libkern/vlop-arm.s // https://bitbucket.org/inferno-os/inferno-os/src/master/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
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