Reviewers: Yang,
Description:
do aligned reads in ContainsOnlyOneByte
[email protected]
BUG=
Please review this at https://codereview.chromium.org/16147004/
SVN Base: https://v8.googlecode.com/svn/branches/bleeding_edge
Affected files:
M src/api.cc
Index: src/api.cc
diff --git a/src/api.cc b/src/api.cc
index
4cdd77ef05a6908c5cc5ebf0fa3398ab0c1f3e72..c950bb8be9825ce0aeaf47750709362c07cf471c
100644
--- a/src/api.cc
+++ b/src/api.cc
@@ -4304,6 +4304,25 @@ bool String::IsOneByte() const {
}
+// Helpers for ContainsOnlyOneByteHelper
+template<size_t size> struct OneByteMask;
+template<> struct OneByteMask<4> {
+ static const uint32_t value = 0xFF00FF00U;
+};
+template<> struct OneByteMask<8> {
+ static const uint64_t value = 0xFF00FF00FF00ULL;
+};
+static const uintptr_t kOneByteMask =
OneByteMask<sizeof(uintptr_t)>::value;
+static const uintptr_t kAlignmentMask = sizeof(uintptr_t) - 1;
+static inline bool Unaligned(const uint16_t* chars) {
+ return reinterpret_cast<const uintptr_t>(chars) & kAlignmentMask;
+}
+static inline const uint16_t* Align(const uint16_t* chars) {
+ return reinterpret_cast<uint16_t*>(
+ reinterpret_cast<uintptr_t>(chars) & ~kAlignmentMask);
+}
+
+
class ContainsOnlyOneByteHelper {
public:
ContainsOnlyOneByteHelper() : is_one_byte_(true) {}
@@ -4315,14 +4334,26 @@ class ContainsOnlyOneByteHelper {
void VisitOneByteString(const uint8_t* chars, int length) {
// Nothing to do.
}
- // TODO(dcarney): do word aligned read.
void VisitTwoByteString(const uint16_t* chars, int length) {
- // Check whole string without breaking.
- uint16_t total = 0;
- for (int i = 0; i < length; i++) {
- total |= chars[i] >> 8;
+ // Accumulated bits.
+ uintptr_t acc = 0;
+ // Align to uintptr_t.
+ const uint16_t* end = chars + length;
+ while (Unaligned(chars) && chars != end) {
+ acc |= *chars++;
+ }
+ // Read word aligned.
+ const uint16_t* aligned_end = Align(end);
+ while (chars < aligned_end) {
+ acc |= *reinterpret_cast<const uintptr_t*>(chars);
+ chars += sizeof(uintptr_t)/sizeof(uint16_t);
+ }
+ // Read the rest.
+ while (chars != end) {
+ acc |= *chars++;
}
- if (total != 0) is_one_byte_ = false;
+ // Check result.
+ if ((acc & kOneByteMask) != 0) is_one_byte_ = false;
}
private:
--
--
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