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[wpiutil] Add LEB128 byte-by-byte reader (#3652)

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This is needed for compatibility with streaming data (e.g. libuv) where partial data
may be received.  Also add raw_ostream writer.
This commit is contained in:
Peter Johnson
2021-10-20 18:50:20 -07:00
committed by GitHub
parent e94397a97d
commit 649a50b401
2 changed files with 81 additions and 4 deletions
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36
wpiutil/src/main/native/cpp/leb128.cpp
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@@ -4,7 +4,10 @@
#include "wpi/leb128.h"
#include "wpi/SpanExtras.h"
#include "wpi/raw_istream.h"
#include "wpi/raw_ostream.h"
#include "wpi/span.h"
namespace wpi {
@@ -21,7 +24,7 @@ uint64_t WriteUleb128(SmallVectorImpl<char>& dest, uint64_t val) {
size_t count = 0;
do {
unsigned char byte = val & 0x7f;
uint8_t byte = val & 0x7f;
val >>= 7;
if (val != 0) {
@@ -35,6 +38,19 @@ uint64_t WriteUleb128(SmallVectorImpl<char>& dest, uint64_t val) {
return count;
}
void WriteUleb128(raw_ostream& os, uint64_t val) {
do {
uint8_t byte = val & 0x7f;
val >>= 7;
if (val != 0) {
byte |= 0x80; // mark this byte to show that more bytes will follow
}
os << byte;
} while (val != 0);
}
uint64_t ReadUleb128(const char* addr, uint64_t* ret) {
uint64_t result = 0;
int shift = 0;
@@ -82,4 +98,22 @@ bool ReadUleb128(raw_istream& is, uint64_t* ret) {
return true;
}
std::optional<uint64_t> Uleb128Reader::ReadOne(span<const uint8_t>* in) {
while (!in->empty()) {
uint8_t byte = in->front();
*in = wpi::drop_front(*in);
m_result |= (byte & 0x7fULL) << m_shift;
m_shift += 7;
if (!(byte & 0x80)) {
uint64_t result = m_result;
m_result = 0;
m_shift = 0;
return result;
}
}
return std::nullopt;
}
} // namespace wpi