/*- * SPDX-License-Identifier: BSD-2-Clause * * Copyright (c) 2024 Getz Mikalsen */ #include #include .weak strncmp .set strncmp, __strncmp .text ENTRY(__strncmp) bic x8, x0, #0xf // x0 aligned to the boundary and x9, x0, #0xf // x9 is the offset bic x10, x1, #0xf // x1 aligned to the boundary and x11, x1, #0xf // x11 is the offset subs x2, x2, #1 b.lo .Lempty mov x13, #-1 // save constants for later mov x16, #0xf /* * Check if either string is located at end of page to avoid crossing * into unmapped page. If so, we load 16 bytes from the nearest * alignment boundary and shift based on the offset. */ add x3, x0, #16 // end of head add x4, x1, #16 eor x3, x3, x0 eor x4, x4, x1 // bits that changed orr x3, x3, x4 // in either str1 or str2 cmp x2,#16 b.lo .Llt16 tbz w3, #PAGE_SHIFT, .Lbegin ldr q0, [x8] // load aligned head ldr q1, [x10] lsl x14, x9, #2 lsl x15, x11, #2 lsl x3, x13, x14 // string head lsl x4, x13, x15 cmeq v5.16b, v0.16b, #0 cmeq v6.16b, v1.16b, #0 shrn v5.8b, v5.8h, #4 shrn v6.8b, v6.8h, #4 fmov x5, d5 fmov x6, d6 adrp x14, shift_data add x14, x14, :lo12:shift_data /* heads may cross page boundary, avoid unmapped loads */ tst x5, x3 b.eq 0f ldr q4, [x14, x9] // load permutation table tbl v0.16b, {v0.16b}, v4.16b b 1f .p2align 4 0: ldr q0, [x0] // load true head 1: tst x6, x4 b.eq 0f ldr q4, [x14, x11] tbl v4.16b, {v1.16b}, v4.16b b 1f .p2align 4 .Lbegin: ldr q0, [x0] // load true heads 0: ldr q4, [x1] 1: cmeq v2.16b, v0.16b, #0 // NUL byte present? cmeq v4.16b, v0.16b, v4.16b // which bytes match? orn v2.16b, v2.16b, v4.16b // mismatch or NUL byte? shrn v2.8b, v2.8h, #4 fmov x5, d2 cbnz x5, .Lhead_mismatch /* load head and second chunk */ ldr q2, [x8, #16] // load second chunk ldr q3, [x10, #16]