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([2804:1b3:a7c1:7e99:f284:be2f:4ee5:d122]) by smtp.gmail.com with ESMTPSA id d18-20020a056830139200b00686467f920bsm6937432otq.48.2023.01.20.13.16.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 20 Jan 2023 13:16:47 -0800 (PST) From: Adhemerval Zanella To: libc-alpha@sourceware.org, Richard Henderson , Noah Goldstein Subject: [PATCH v10 09/24] string: Improve generic strncmp Date: Fri, 20 Jan 2023 18:16:07 -0300 Message-Id: <20230120211622.3445279-10-adhemerval.zanella@linaro.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20230120211622.3445279-1-adhemerval.zanella@linaro.org> References: <20230120211622.3445279-1-adhemerval.zanella@linaro.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Spam-Status: No, score=-12.7 required=5.0 tests=BAYES_00,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,GIT_PATCH_0,KAM_SHORT,RCVD_IN_DNSWL_NONE,SPF_HELO_NONE,SPF_PASS,TXREP autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: New generic implementation tries to use word operations along with the new string-fz{b,i} functions even for inputs with different alignments (with still uses aligned access plus merge operation to get a correct word by word comparison). Checked on x86_64-linux-gnu, i686-linux-gnu, powerpc64-linux-gnu, and powerpc-linux-gnu by removing the arch-specific assembly implementation and disabling multi-arch (it covers both LE and BE for 64 and 32 bits). --- string/strcmp-impl.h | 41 ++++++++++++++ string/strcmp.c | 23 ++------ string/strncmp.c | 130 +++++++++++++++++++++++++++++++------------ 3 files changed, 138 insertions(+), 56 deletions(-) create mode 100644 string/strcmp-impl.h diff --git a/string/strcmp-impl.h b/string/strcmp-impl.h new file mode 100644 index 0000000000..618240368a --- /dev/null +++ b/string/strcmp-impl.h @@ -0,0 +1,41 @@ +/* Common definition for string compare implementations. + Copyright (C) 2023 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + . */ + +#ifndef _STRCMP_IMPL_H +#define _STRCMP_IMPL_H + +#include +#include + +static inline int +final_cmp (const op_t w1, const op_t w2, size_t n) +{ + /* It can not use index_first_zero_ne because it must not compare past the + final '\0' is present (and final_cmp is called before has_zero check). + */ + for (size_t i = 0; i < n; i++) + { + unsigned char c1 = extractbyte (w1, i); + unsigned char c2 = extractbyte (w2, i); + if (c1 == '\0' || c1 != c2) + return c1 - c2; + } + return 0; +} + +#endif diff --git a/string/strcmp.c b/string/strcmp.c index 42e24242b6..8e7b3310db 100644 --- a/string/strcmp.c +++ b/string/strcmp.c @@ -16,6 +16,7 @@ . */ #include +#include #include #include #include @@ -25,22 +26,6 @@ # define strcmp STRCMP #endif -static inline int -final_cmp (const op_t w1, const op_t w2) -{ - /* It can not use index_first_zero_ne because it must not compare past the - final '\0' is present (and final_cmp is called before has_zero check). - */ - for (size_t i = 0; i < sizeof (op_t); i++) - { - unsigned char c1 = extractbyte (w1, i); - unsigned char c2 = extractbyte (w2, i); - if (c1 == '\0' || c1 != c2) - return c1 - c2; - } - return 0; -} - /* Aligned loop: if a difference is found, exit to compare the bytes. Else if a zero is found we have equal strings. */ static inline int @@ -56,7 +41,7 @@ strcmp_aligned_loop (const op_t *x1, const op_t *x2, op_t w1) w2 = *x2++; } - return final_cmp (w1, w2); + return final_cmp (w1, w2, sizeof (op_t)); } /* Unaligned loop: align the first partial of P2, with 0xff for the rest of @@ -83,7 +68,7 @@ strcmp_unaligned_loop (const op_t *x1, const op_t *x2, op_t w1, uintptr_t ofs) w2b = *x2++; w2 = MERGE (w2a, sh_1, w2b, sh_2); if (w1 != w2) - return final_cmp (w1, w2); + return final_cmp (w1, w2, sizeof (op_t)); if (has_zero (w2b)) break; w1 = *x1++; @@ -100,7 +85,7 @@ strcmp_unaligned_loop (const op_t *x1, const op_t *x2, op_t w1, uintptr_t ofs) w2 = MERGE (w2b, sh_1, 0, sh_2); } - return final_cmp (w1, w2); + return final_cmp (w1, w2, sizeof (op_t)); } /* Compare S1 and S2, returning less than, equal to or diff --git a/string/strncmp.c b/string/strncmp.c index fd7cee09b6..3e6040df09 100644 --- a/string/strncmp.c +++ b/string/strncmp.c @@ -15,7 +15,13 @@ License along with the GNU C Library; if not, see . */ +#include +#include +#include +#include +#include #include +#include #include #undef strncmp @@ -24,51 +30,101 @@ #define STRNCMP strncmp #endif -/* Compare no more than N characters of S1 and S2, - returning less than, equal to or greater than zero - if S1 is lexicographically less than, equal to or - greater than S2. */ -int -STRNCMP (const char *s1, const char *s2, size_t n) +/* Aligned loop: if a difference is found, exit to compare the bytes. Else + if a zero is found we have equal strings. */ +static inline int +strncmp_aligned_loop (const op_t *x1, const op_t *x2, op_t w1, size_t n) { - unsigned char c1 = '\0'; - unsigned char c2 = '\0'; + op_t w2 = *x2++; - if (n >= 4) + while (w1 == w2) { - size_t n4 = n >> 2; - do - { - c1 = (unsigned char) *s1++; - c2 = (unsigned char) *s2++; - if (c1 == '\0' || c1 != c2) - return c1 - c2; - c1 = (unsigned char) *s1++; - c2 = (unsigned char) *s2++; - if (c1 == '\0' || c1 != c2) - return c1 - c2; - c1 = (unsigned char) *s1++; - c2 = (unsigned char) *s2++; - if (c1 == '\0' || c1 != c2) - return c1 - c2; - c1 = (unsigned char) *s1++; - c2 = (unsigned char) *s2++; - if (c1 == '\0' || c1 != c2) - return c1 - c2; - } while (--n4 > 0); - n &= 3; + if (n <= sizeof (op_t)) + break; + n -= sizeof (op_t); + + if (has_zero (w1)) + return 0; + w1 = *x1++; + w2 = *x2++; } - while (n > 0) + return final_cmp (w1, w2, n); +} + +/* Unaligned loop: align the first partial of P2, with 0xff for the rest of + the bytes so that we can also apply the has_zero test to see if we have + already reached EOS. If we have, then we can simply fall through to the + final comparison. */ +static inline int +strncmp_unaligned_loop (const op_t *x1, const op_t *x2, op_t w1, uintptr_t ofs, + size_t n) +{ + op_t w2a = *x2++; + uintptr_t sh_1 = ofs * CHAR_BIT; + uintptr_t sh_2 = sizeof(op_t) * CHAR_BIT - sh_1; + + op_t w2 = MERGE (w2a, sh_1, (op_t)-1, sh_2); + if (!has_zero (w2) && n > (sizeof (op_t) - ofs)) { - c1 = (unsigned char) *s1++; - c2 = (unsigned char) *s2++; - if (c1 == '\0' || c1 != c2) - return c1 - c2; - n--; + op_t w2b; + + /* Unaligned loop. The invariant is that W2B, which is "ahead" of W1, + does not contain end-of-string. Therefore it is safe (and necessary) + to read another word from each while we do not have a difference. */ + while (1) + { + w2b = *x2++; + w2 = MERGE (w2a, sh_1, w2b, sh_2); + if (n <= sizeof (op_t) || w1 != w2) + return final_cmp (w1, w2, n); + n -= sizeof(op_t); + if (has_zero (w2b) || n <= (sizeof (op_t) - ofs)) + break; + w1 = *x1++; + w2a = w2b; + } + + /* Zero found in the second partial of P2. If we had EOS in the aligned + word, we have equality. */ + if (has_zero (w1)) + return 0; + + /* Load the final word of P1 and align the final partial of P2. */ + w1 = *x1++; + w2 = MERGE (w2b, sh_1, 0, sh_2); } - return c1 - c2; + return final_cmp (w1, w2, n); } +/* Compare no more than N characters of S1 and S2, + returning less than, equal to or greater than zero + if S1 is lexicographically less than, equal to or + greater than S2. */ +int +STRNCMP (const char *p1, const char *p2, size_t n) +{ + /* Handle the unaligned bytes of p1 first. */ + uintptr_t a = MIN (-(uintptr_t)p1 % sizeof(op_t), n); + int diff = 0; + for (int i = 0; i < a; ++i) + { + unsigned char c1 = *p1++; + unsigned char c2 = *p2++; + diff = c1 - c2; + if (c1 == '\0' || diff != 0) + return diff; + } + if (a == n) + return diff; + + /* P1 is now aligned to op_t. P2 may or may not be. */ + const op_t *x1 = (const op_t *) p1; + op_t w1 = *x1++; + uintptr_t ofs = (uintptr_t) p2 % sizeof(op_t); + return ofs == 0 + ? strncmp_aligned_loop (x1, (const op_t *) p2, w1, n - a) + : strncmp_unaligned_loop (x1, (const op_t *) (p2 - ofs), w1, ofs, n - a); +} libc_hidden_builtin_def (STRNCMP) -- 2.34.1