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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 | /* * memcpy - copy memory area * * Copyright (c) 2012-2020, Arm Limited. * SPDX-License-Identifier: MIT */ /* Assumptions: * * ARMv8-a, AArch64, unaligned accesses. * */ #define dstin x0 #define src x1 #define count x2 #define dst x3 #define srcend x4 #define dstend x5 #define A_l x6 #define A_lw w6 #define A_h x7 #define B_l x8 #define B_lw w8 #define B_h x9 #define C_l x10 #define C_lw w10 #define C_h x11 #define D_l x12 #define D_h x13 #define E_l x14 #define E_h x15 #define F_l x16 #define F_h x17 #define G_l count #define G_h dst #define H_l src #define H_h srcend #define tmp1 x14 /* This implementation of memcpy uses unaligned accesses and branchless sequences to keep the code small, simple and improve performance. Copies are split into 3 main cases: small copies of up to 32 bytes, medium copies of up to 128 bytes, and large copies. The overhead of the overlap check is negligible since it is only required for large copies. Large copies use a software pipelined loop processing 64 bytes per iteration. The destination pointer is 16-byte aligned to minimize unaligned accesses. The loop tail is handled by always copying 64 bytes from the end. */ .global memcpy .type memcpy,%function memcpy: add srcend, src, count add dstend, dstin, count cmp count, 128 b.hi .Lcopy_long cmp count, 32 b.hi .Lcopy32_128 /* Small copies: 0..32 bytes. */ cmp count, 16 b.lo .Lcopy16 ldp A_l, A_h, [src] ldp D_l, D_h, [srcend, -16] stp A_l, A_h, [dstin] stp D_l, D_h, [dstend, -16] ret /* Copy 8-15 bytes. */ .Lcopy16: tbz count, 3, .Lcopy8 ldr A_l, [src] ldr A_h, [srcend, -8] str A_l, [dstin] str A_h, [dstend, -8] ret .p2align 3 /* Copy 4-7 bytes. */ .Lcopy8: tbz count, 2, .Lcopy4 ldr A_lw, [src] ldr B_lw, [srcend, -4] str A_lw, [dstin] str B_lw, [dstend, -4] ret /* Copy 0..3 bytes using a branchless sequence. */ .Lcopy4: cbz count, .Lcopy0 lsr tmp1, count, 1 ldrb A_lw, [src] ldrb C_lw, [srcend, -1] ldrb B_lw, [src, tmp1] strb A_lw, [dstin] strb B_lw, [dstin, tmp1] strb C_lw, [dstend, -1] .Lcopy0: ret .p2align 4 /* Medium copies: 33..128 bytes. */ .Lcopy32_128: ldp A_l, A_h, [src] ldp B_l, B_h, [src, 16] ldp C_l, C_h, [srcend, -32] ldp D_l, D_h, [srcend, -16] cmp count, 64 b.hi .Lcopy128 stp A_l, A_h, [dstin] stp B_l, B_h, [dstin, 16] stp C_l, C_h, [dstend, -32] stp D_l, D_h, [dstend, -16] ret .p2align 4 /* Copy 65..128 bytes. */ .Lcopy128: ldp E_l, E_h, [src, 32] ldp F_l, F_h, [src, 48] cmp count, 96 b.ls .Lcopy96 ldp G_l, G_h, [srcend, -64] ldp H_l, H_h, [srcend, -48] stp G_l, G_h, [dstend, -64] stp H_l, H_h, [dstend, -48] .Lcopy96: stp A_l, A_h, [dstin] stp B_l, B_h, [dstin, 16] stp E_l, E_h, [dstin, 32] stp F_l, F_h, [dstin, 48] stp C_l, C_h, [dstend, -32] stp D_l, D_h, [dstend, -16] ret .p2align 4 /* Copy more than 128 bytes. */ .Lcopy_long: /* Copy 16 bytes and then align dst to 16-byte alignment. */ ldp D_l, D_h, [src] and tmp1, dstin, 15 bic dst, dstin, 15 sub src, src, tmp1 add count, count, tmp1 /* Count is now 16 too large. */ ldp A_l, A_h, [src, 16] stp D_l, D_h, [dstin] ldp B_l, B_h, [src, 32] ldp C_l, C_h, [src, 48] ldp D_l, D_h, [src, 64]! subs count, count, 128 + 16 /* Test and readjust count. */ b.ls .Lcopy64_from_end .Lloop64: stp A_l, A_h, [dst, 16] ldp A_l, A_h, [src, 16] stp B_l, B_h, [dst, 32] ldp B_l, B_h, [src, 32] stp C_l, C_h, [dst, 48] ldp C_l, C_h, [src, 48] stp D_l, D_h, [dst, 64]! ldp D_l, D_h, [src, 64]! subs count, count, 64 b.hi .Lloop64 /* Write the last iteration and copy 64 bytes from the end. */ .Lcopy64_from_end: ldp E_l, E_h, [srcend, -64] stp A_l, A_h, [dst, 16] ldp A_l, A_h, [srcend, -48] stp B_l, B_h, [dst, 32] ldp B_l, B_h, [srcend, -32] stp C_l, C_h, [dst, 48] ldp C_l, C_h, [srcend, -16] stp D_l, D_h, [dst, 64] stp E_l, E_h, [dstend, -64] stp A_l, A_h, [dstend, -48] stp B_l, B_h, [dstend, -32] stp C_l, C_h, [dstend, -16] ret .size memcpy,.-memcpy |