Index: src/string-case.cc |
diff --git a/src/string-case.cc b/src/string-case.cc |
new file mode 100644 |
index 0000000000000000000000000000000000000000..52d963608306d30592204a3ab16c5d5b443a1c54 |
--- /dev/null |
+++ b/src/string-case.cc |
@@ -0,0 +1,130 @@ |
+// 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('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 |