Felix-Gong commented on code in PR #3390: URL: https://github.com/apache/brpc/pull/3390#discussion_r3600792260
########## src/butil/string_compare_rvv.cc: ########## @@ -0,0 +1,105 @@ +/* -*- mode: c; c-basic-offset: 4; indent-tabs-mode: nil; tab-width: 4 -*- */ +/* vi: set expandtab shiftwidth=4 tabstop=4: */ +/** + * \file + * RISC-V Vector (RVV) accelerated memcmp/memchr for StringPiece operations. + * + * Algorithm follows glibc's RVV memcmp/memchr patterns: + * - Use vsetvli with e8/m8 for maximum throughput (hardware-adaptive VL) + * - Use vfirst.m to find first differing/matching byte (no vcpop needed) + * - Simple loop: load → compare → find first → branch + * + * Licensed to the Apache Software Foundation (ASF) under one + * or more contributor license agreements. See the NOTICE file + * distributed with this work for additional information + * regarding copyright ownership. The ASF licenses this file + * to you under the Apache License, Version 2.0 (the + * License); you may not use this file except in compliance + * with the License. You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, + * software distributed under the License is distributed on an + * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY + * KIND, either express or implied. See the License for the + * specific language governing permissions and limitations + * under the License. + */ + +#include "butil/strings/string_piece.h" + +#if defined(__riscv) && defined(__riscv_vector) +#include <riscv_vector.h> +#include <stdint.h> +#include <string.h> + +namespace butil { + +/** + * rvv_memcmp - RVV-accelerated byte comparison following glibc pattern. + * + * Compares two byte arrays and returns: + * < 0 if p1 < p2 + * 0 if p1 == p2 + * > 0 if p1 > p2 + * + * Uses RVV m8 with hardware-adaptive VL for maximum throughput. + */ +int rvv_memcmp(const void* p1, const void* p2, size_t n) { + const uint8_t* src1 = static_cast<const uint8_t*>(p1); + const uint8_t* src2 = static_cast<const uint8_t*>(p2); + size_t remaining = n; + + while (remaining > 0) { + size_t vl = __riscv_vsetvl_e8m8(remaining); + vuint8m8_t v1 = __riscv_vle8_v_u8m8(src1, vl); + vuint8m8_t v2 = __riscv_vle8_v_u8m8(src2, vl); + vbool1_t neq = __riscv_vmsne_vv_u8m8_b1(v1, v2, vl); + long first = __riscv_vfirst_m_b1(neq, vl); + + if (first >= 0) { + uint8_t b1 = src1[first]; + uint8_t b2 = src2[first]; + return (b1 < b2) ? -1 : 1; + } Review Comment: Fixed. Changed to return static_cast<int>(src1[first]) - static_cast<int>(src2[first]); which matches glibc memcmp semantics and preserves the byte-difference contract expected by traits_type::compare. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
