| // Copyright 2016 the V8 project authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| #include "src/string-case.h" |
| |
| #include "src/assert-scope.h" |
| #include "src/base/logging.h" |
| #include "src/globals.h" |
| #include "src/utils.h" |
| |
| namespace v8 { |
| namespace internal { |
| |
| #ifdef DEBUG |
| bool CheckFastAsciiConvert(char* dst, const char* src, int length, bool changed, |
| bool is_to_lower) { |
| bool expected_changed = false; |
| for (int i = 0; i < length; i++) { |
| if (dst[i] == src[i]) continue; |
| expected_changed = true; |
| if (is_to_lower) { |
| DCHECK('A' <= src[i] && src[i] <= 'Z'); |
| DCHECK(dst[i] == src[i] + ('a' - 'A')); |
| } else { |
| DCHECK('a' <= src[i] && src[i] <= 'z'); |
| DCHECK(dst[i] == src[i] - ('a' - 'A')); |
| } |
| } |
| return (expected_changed == changed); |
| } |
| #endif |
| |
| const uintptr_t kOneInEveryByte = kUintptrAllBitsSet / 0xFF; |
| const uintptr_t kAsciiMask = kOneInEveryByte << 7; |
| |
| // Given a word and two range boundaries returns a word with high bit |
| // set in every byte iff the corresponding input byte was strictly in |
| // the range (m, n). All the other bits in the result are cleared. |
| // This function is only useful when it can be inlined and the |
| // boundaries are statically known. |
| // Requires: all bytes in the input word and the boundaries must be |
| // ASCII (less than 0x7F). |
| static inline uintptr_t AsciiRangeMask(uintptr_t w, char m, char n) { |
| // Use strict inequalities since in edge cases the function could be |
| // further simplified. |
| DCHECK(0 < m && m < n); |
| // Has high bit set in every w byte less than n. |
| uintptr_t tmp1 = kOneInEveryByte * (0x7F + n) - w; |
| // Has high bit set in every w byte greater than m. |
| uintptr_t tmp2 = w + kOneInEveryByte * (0x7F - m); |
| return (tmp1 & tmp2 & (kOneInEveryByte * 0x80)); |
| } |
| |
| template <bool is_lower> |
| int FastAsciiConvert(char* dst, const char* src, int length, |
| bool* changed_out) { |
| #ifdef DEBUG |
| char* saved_dst = dst; |
| #endif |
| const char* saved_src = src; |
| DisallowHeapAllocation no_gc; |
| // We rely on the distance between upper and lower case letters |
| // being a known power of 2. |
| DCHECK_EQ('a' - 'A', 1 << 5); |
| // Boundaries for the range of input characters than require conversion. |
| static const char lo = is_lower ? 'A' - 1 : 'a' - 1; |
| static const char hi = is_lower ? 'Z' + 1 : 'z' + 1; |
| bool changed = false; |
| const char* const limit = src + length; |
| |
| // dst is newly allocated and always aligned. |
| DCHECK(IsAligned(reinterpret_cast<intptr_t>(dst), sizeof(uintptr_t))); |
| // Only attempt processing one word at a time if src is also aligned. |
| if (IsAligned(reinterpret_cast<intptr_t>(src), sizeof(uintptr_t))) { |
| // Process the prefix of the input that requires no conversion one aligned |
| // (machine) word at a time. |
| while (src <= limit - sizeof(uintptr_t)) { |
| const uintptr_t w = *reinterpret_cast<const uintptr_t*>(src); |
| if ((w & kAsciiMask) != 0) return static_cast<int>(src - saved_src); |
| if (AsciiRangeMask(w, lo, hi) != 0) { |
| changed = true; |
| break; |
| } |
| *reinterpret_cast<uintptr_t*>(dst) = w; |
| src += sizeof(uintptr_t); |
| dst += sizeof(uintptr_t); |
| } |
| // Process the remainder of the input performing conversion when |
| // required one word at a time. |
| while (src <= limit - sizeof(uintptr_t)) { |
| const uintptr_t w = *reinterpret_cast<const uintptr_t*>(src); |
| if ((w & kAsciiMask) != 0) return static_cast<int>(src - saved_src); |
| uintptr_t m = AsciiRangeMask(w, lo, hi); |
| // The mask has high (7th) bit set in every byte that needs |
| // conversion and we know that the distance between cases is |
| // 1 << 5. |
| *reinterpret_cast<uintptr_t*>(dst) = w ^ (m >> 2); |
| src += sizeof(uintptr_t); |
| dst += sizeof(uintptr_t); |
| } |
| } |
| // Process the last few bytes of the input (or the whole input if |
| // unaligned access is not supported). |
| while (src < limit) { |
| char c = *src; |
| if ((c & kAsciiMask) != 0) return static_cast<int>(src - saved_src); |
| if (lo < c && c < hi) { |
| c ^= (1 << 5); |
| changed = true; |
| } |
| *dst = c; |
| ++src; |
| ++dst; |
| } |
| |
| DCHECK( |
| CheckFastAsciiConvert(saved_dst, saved_src, length, changed, is_lower)); |
| |
| *changed_out = changed; |
| return length; |
| } |
| |
| template int FastAsciiConvert<false>(char* dst, const char* src, int length, |
| bool* changed_out); |
| template int FastAsciiConvert<true>(char* dst, const char* src, int length, |
| bool* changed_out); |
| |
| } // namespace internal |
| } // namespace v8 |