Delta-encoding of mapping tables.
Both PC offsets and dalvik offsets are delta-encoded. Since
PC offsets are increasing, the deltas are then compressed as
unsigned LEB128. Dalvik offsets are not monotonic, so their
deltas are compressed as signed LEB128.
This reduces the size of the mapping tables by about 30%
on average, 25% from the PC offset and 5% from the dalvik
offset delta encoding.
Bug: 9437697
Change-Id: I600ab9c22dec178088d4947a811cca3bc8bd4cf4
diff --git a/compiler/leb128_encoder.h b/compiler/leb128_encoder.h
index e9a1c32..fe38c2f 100644
--- a/compiler/leb128_encoder.h
+++ b/compiler/leb128_encoder.h
@@ -18,33 +18,54 @@
#define ART_COMPILER_LEB128_ENCODER_H_
#include "base/macros.h"
+#include "leb128.h"
namespace art {
// An encoder with an API similar to vector<uint32_t> where the data is captured in ULEB128 format.
-class UnsignedLeb128EncodingVector {
+class Leb128EncodingVector {
public:
- UnsignedLeb128EncodingVector() {
+ Leb128EncodingVector() {
}
- void PushBack(uint32_t value) {
- bool done = false;
- do {
- uint8_t out = value & 0x7f;
- if (out != value) {
- data_.push_back(out | 0x80);
- value >>= 7;
- } else {
- data_.push_back(out);
- done = true;
- }
- } while (!done);
+ void Reserve(uint32_t size) {
+ data_.reserve(size);
+ }
+
+ void PushBackUnsigned(uint32_t value) {
+ uint8_t out = value & 0x7f;
+ value >>= 7;
+ while (value != 0) {
+ data_.push_back(out | 0x80);
+ out = value & 0x7f;
+ value >>= 7;
+ }
+ data_.push_back(out);
}
template<typename It>
- void InsertBack(It cur, It end) {
+ void InsertBackUnsigned(It cur, It end) {
for (; cur != end; ++cur) {
- PushBack(*cur);
+ PushBackUnsigned(*cur);
+ }
+ }
+
+ void PushBackSigned(int32_t value) {
+ uint32_t extra_bits = static_cast<uint32_t>(value ^ (value >> 31)) >> 6;
+ uint8_t out = value & 0x7f;
+ while (extra_bits != 0u) {
+ data_.push_back(out | 0x80);
+ value >>= 7;
+ out = value & 0x7f;
+ extra_bits >>= 7;
+ }
+ data_.push_back(out);
+ }
+
+ template<typename It>
+ void InsertBackSigned(It cur, It end) {
+ for (; cur != end; ++cur) {
+ PushBackSigned(*cur);
}
}
@@ -55,7 +76,7 @@
private:
std::vector<uint8_t> data_;
- DISALLOW_COPY_AND_ASSIGN(UnsignedLeb128EncodingVector);
+ DISALLOW_COPY_AND_ASSIGN(Leb128EncodingVector);
};
} // namespace art