LEB128.h

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//===- llvm/Support/LEB128.h - [SU]LEB128 utility functions -----*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file declares some utility functions for encoding SLEB128 and
// ULEB128 values.
//
//===----------------------------------------------------------------------===//
 
#ifndef LLVM_SUPPORT_LEB128_H
#define LLVM_SUPPORT_LEB128_H
 
#include "llvm/Support/raw_ostream.h"
 
namespace llvm {
 
/// Utility function to encode a SLEB128 value to an output stream. Returns
/// the length in bytes of the encoded value.
inline unsigned encodeSLEB128(int64_t Value, raw_ostream &OS,
                              unsigned PadTo = 0) {
  bool More;
  unsigned Count = 0;
  do {
    uint8_t Byte = Value & 0x7f;
    // NOTE: this assumes that this signed shift is an arithmetic right shift.
    Value >>= 7;
    More = !((((Value == 0 ) && ((Byte & 0x40) == 0)) ||
              ((Value == -1) && ((Byte & 0x40) != 0))));
    Count++;
    if (More || Count < PadTo)
      Byte |= 0x80; // Mark this byte to show that more bytes will follow.
    OS << char(Byte);
  } while (More);
 
  // Pad with 0x80 and emit a terminating byte at the end.
  if (Count < PadTo) {
    uint8_t PadValue = Value < 0 ? 0x7f : 0x00;
    for (; Count < PadTo - 1; ++Count)
      OS << char(PadValue | 0x80);
    OS << char(PadValue);
    Count++;
  }
  return Count;
}
 
/// Utility function to encode a SLEB128 value to a buffer. Returns
/// the length in bytes of the encoded value.
inline unsigned encodeSLEB128(int64_t Value, uint8_t *p, unsigned PadTo = 0) {
  uint8_t *orig_p = p;
  unsigned Count = 0;
  bool More;
  do {
    uint8_t Byte = Value & 0x7f;
    // NOTE: this assumes that this signed shift is an arithmetic right shift.
    Value >>= 7;
    More = !((((Value == 0 ) && ((Byte & 0x40) == 0)) ||
              ((Value == -1) && ((Byte & 0x40) != 0))));
    Count++;
    if (More || Count < PadTo)
      Byte |= 0x80; // Mark this byte to show that more bytes will follow.
    *p++ = Byte;
  } while (More);
 
  // Pad with 0x80 and emit a terminating byte at the end.
  if (Count < PadTo) {
    uint8_t PadValue = Value < 0 ? 0x7f : 0x00;
    for (; Count < PadTo - 1; ++Count)
      *p++ = (PadValue | 0x80);
    *p++ = PadValue;
  }
  return (unsigned)(p - orig_p);
}
 
/// Utility function to encode a ULEB128 value to an output stream. Returns
/// the length in bytes of the encoded value.
inline unsigned encodeULEB128(uint64_t Value, raw_ostream &OS,
                              unsigned PadTo = 0) {
  unsigned Count = 0;
  do {
    uint8_t Byte = Value & 0x7f;
    Value >>= 7;
    Count++;
    if (Value != 0 || Count < PadTo)
      Byte |= 0x80; // Mark this byte to show that more bytes will follow.
    OS << char(Byte);
  } while (Value != 0);
 
  // Pad with 0x80 and emit a null byte at the end.
  if (Count < PadTo) {
    for (; Count < PadTo - 1; ++Count)
      OS << '\x80';
    OS << '\x00';
    Count++;
  }
  return Count;
}
 
/// Utility function to encode a ULEB128 value to a buffer. Returns
/// the length in bytes of the encoded value.
inline unsigned encodeULEB128(uint64_t Value, uint8_t *p,
                              unsigned PadTo = 0) {
  uint8_t *orig_p = p;
  unsigned Count = 0;
  do {
    uint8_t Byte = Value & 0x7f;
    Value >>= 7;
    Count++;
    if (Value != 0 || Count < PadTo)
      Byte |= 0x80; // Mark this byte to show that more bytes will follow.
    *p++ = Byte;
  } while (Value != 0);
 
  // Pad with 0x80 and emit a null byte at the end.
  if (Count < PadTo) {
    for (; Count < PadTo - 1; ++Count)
      *p++ = '\x80';
    *p++ = '\x00';
  }
 
  return (unsigned)(p - orig_p);
}
 
/// Utility function to decode a ULEB128 value.
inline uint64_t decodeULEB128(const uint8_t *p, unsigned *n = nullptr,
                              const uint8_t *end = nullptr,
                              const char **error = nullptr) {
  const uint8_t *orig_p = p;
  uint64_t Value = 0;
  unsigned Shift = 0;
  if (error)
    *error = nullptr;
  do {
    if (p == end) {
      if (error)
        *error = "malformed uleb128, extends past end";
      if (n)
        *n = (unsigned)(p - orig_p);
      return 0;
    }
    uint64_t Slice = *p & 0x7f;
    if ((Shift >= 64 && Slice != 0) || Slice << Shift >> Shift != Slice) {
      if (error)
        *error = "uleb128 too big for uint64";
      if (n)
        *n = (unsigned)(p - orig_p);
      return 0;
    }
    Value += Slice << Shift;
    Shift += 7;
  } while (*p++ >= 128);
  if (n)
    *n = (unsigned)(p - orig_p);
  return Value;
}
 
/// Utility function to decode a SLEB128 value.
inline int64_t decodeSLEB128(const uint8_t *p, unsigned *n = nullptr,
                             const uint8_t *end = nullptr,
                             const char **error = nullptr) {
  const uint8_t *orig_p = p;
  int64_t Value = 0;
  unsigned Shift = 0;
  uint8_t Byte;
  if (error)
    *error = nullptr;
  do {
    if (p == end) {
      if (error)
        *error = "malformed sleb128, extends past end";
      if (n)
        *n = (unsigned)(p - orig_p);
      return 0;
    }
    Byte = *p;
    uint64_t Slice = Byte & 0x7f;
    if ((Shift >= 64 && Slice != (Value < 0 ? 0x7f : 0x00)) ||
        (Shift == 63 && Slice != 0 && Slice != 0x7f)) {
      if (error)
        *error = "sleb128 too big for int64";
      if (n)
        *n = (unsigned)(p - orig_p);
      return 0;
    }
    Value |= Slice << Shift;
    Shift += 7;
    ++p;
  } while (Byte >= 128);
  // Sign extend negative numbers if needed.
  if (Shift < 64 && (Byte & 0x40))
    Value |= UINT64_MAX << Shift;
  if (n)
    *n = (unsigned)(p - orig_p);
  return Value;
}
 
/// Utility function to get the size of the ULEB128-encoded value.
extern unsigned getULEB128Size(uint64_t Value);
 
/// Utility function to get the size of the SLEB128-encoded value.
extern unsigned getSLEB128Size(int64_t Value);
 
} // namespace llvm
 
#endif // LLVM_SUPPORT_LEB128_H