folly-2021.12.27.00/folly/String.cpp

/*
 * Copyright (c) Facebook, Inc. and its affiliates.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include <folly/String.h>

#include <cctype>
#include <cerrno>
#include <cstdarg>
#include <cstring>
#include <iterator>
#include <sstream>
#include <stdexcept>

#include <glog/logging.h>

#include <folly/Portability.h>
#include <folly/ScopeGuard.h>
#include <folly/container/Array.h>

namespace folly {

static_assert(IsConvertible<float>::value, "");
static_assert(IsConvertible<int>::value, "");
static_assert(IsConvertible<bool>::value, "");
static_assert(IsConvertible<int>::value, "");
static_assert(!IsConvertible<std::vector<int>>::value, "");

namespace detail {

struct string_table_c_escape_make_item {
  constexpr char operator()(std::size_t index) const {
    // clang-format off
    return
        index == '"' ? '"' :
        index == '\\' ? '\\' :
        index == '?' ? '?' :
        index == '\n' ? 'n' :
        index == '\r' ? 'r' :
        index == '\t' ? 't' :
        index < 32 || index > 126 ? 'O' : // octal
        'P'; // printable
    // clang-format on
  }
};

struct string_table_c_unescape_make_item {
  constexpr char operator()(std::size_t index) const {
    // clang-format off
    return
        index == '\'' ? '\'' :
        index == '?' ? '?' :
        index == '\\' ? '\\' :
        index == '"' ? '"' :
        index == 'a' ? '\a' :
        index == 'b' ? '\b' :
        index == 'f' ? '\f' :
        index == 'n' ? '\n' :
        index == 'r' ? '\r' :
        index == 't' ? '\t' :
        index == 'v' ? '\v' :
        index >= '0' && index <= '7' ? 'O' : // octal
        index == 'x' ? 'X' : // hex
        'I'; // invalid
    // clang-format on
  }
};

struct string_table_hex_make_item {
  constexpr unsigned char operator()(std::size_t index) const {
    // clang-format off
    return static_cast<unsigned char>(
        index >= '0' && index <= '9' ? index - '0' :
        index >= 'a' && index <= 'f' ? index - 'a' + 10 :
        index >= 'A' && index <= 'F' ? index - 'A' + 10 :
        16);
    // clang-format on
  }
};

struct string_table_uri_escape_make_item {
  //  0 = passthrough
  //  1 = unused
  //  2 = safe in path (/)
  //  3 = space (replace with '+' in query)
  //  4 = always percent-encode
  constexpr unsigned char operator()(std::size_t index) const {
    // clang-format off
    return
        index >= '0' && index <= '9' ? 0 :
        index >= 'A' && index <= 'Z' ? 0 :
        index >= 'a' && index <= 'z' ? 0 :
        index == '-' ? 0 :
        index == '_' ? 0 :
        index == '.' ? 0 :
        index == '~' ? 0 :
        index == '/' ? 2 :
        index == ' ' ? 3 :
        4;
    // clang-format on
  }
};

FOLLY_STORAGE_CONSTEXPR decltype(cEscapeTable) cEscapeTable =
    make_array_with<256>(string_table_c_escape_make_item{});
FOLLY_STORAGE_CONSTEXPR decltype(cUnescapeTable) cUnescapeTable =
    make_array_with<256>(string_table_c_unescape_make_item{});
FOLLY_STORAGE_CONSTEXPR decltype(hexTable) hexTable =
    make_array_with<256>(string_table_hex_make_item{});
FOLLY_STORAGE_CONSTEXPR decltype(uriEscapeTable) uriEscapeTable =
    make_array_with<256>(string_table_uri_escape_make_item{});

} // namespace detail

static inline bool is_oddspace(char c) {
  return c == '\n' || c == '\t' || c == '\r';
}

StringPiece ltrimWhitespace(StringPiece sp) {
  // Spaces other than ' ' characters are less common but should be
  // checked.  This configuration where we loop on the ' '
  // separately from oddspaces was empirically fastest.

  while (true) {
    while (!sp.empty() && sp.front() == ' ') {
      sp.pop_front();
    }
    if (!sp.empty() && is_oddspace(sp.front())) {
      sp.pop_front();
      continue;
    }

    return sp;
  }
}

StringPiece rtrimWhitespace(StringPiece sp) {
  // Spaces other than ' ' characters are less common but should be
  // checked.  This configuration where we loop on the ' '
  // separately from oddspaces was empirically fastest.

  while (true) {
    while (!sp.empty() && sp.back() == ' ') {
      sp.pop_back();
    }
    if (!sp.empty() && is_oddspace(sp.back())) {
      sp.pop_back();
      continue;
    }

    return sp;
  }
}

namespace {

int stringAppendfImplHelper(
    char* buf, size_t bufsize, const char* format, va_list args) {
  va_list args_copy;
  va_copy(args_copy, args);
  int bytes_used = vsnprintf(buf, bufsize, format, args_copy);
  va_end(args_copy);
  return bytes_used;
}

void stringAppendfImpl(std::string& output, const char* format, va_list args) {
  // Very simple; first, try to avoid an allocation by using an inline
  // buffer.  If that fails to hold the output string, allocate one on
  // the heap, use it instead.
  //
  // It is hard to guess the proper size of this buffer; some
  // heuristics could be based on the number of format characters, or
  // static analysis of a codebase.  Or, we can just pick a number
  // that seems big enough for simple cases (say, one line of text on
  // a terminal) without being large enough to be concerning as a
  // stack variable.
  std::array<char, 128> inline_buffer;

  int bytes_used = stringAppendfImplHelper(
      inline_buffer.data(), inline_buffer.size(), format, args);
  if (bytes_used < 0) {
    throw std::runtime_error(to<std::string>(
        "Invalid format string; snprintf returned negative "
        "with format string: ",
        format));
  }

  if (static_cast<size_t>(bytes_used) < inline_buffer.size()) {
    output.append(inline_buffer.data(), size_t(bytes_used));
    return;
  }

  // Couldn't fit.  Heap allocate a buffer, oh well.
  std::unique_ptr<char[]> heap_buffer(new char[size_t(bytes_used + 1)]);
  int final_bytes_used = stringAppendfImplHelper(
      heap_buffer.get(), size_t(bytes_used + 1), format, args);
  // The second call can take fewer bytes if, for example, we were printing a
  // string buffer with null-terminating char using a width specifier -
  // vsnprintf("%.*s", buf.size(), buf)
  CHECK(bytes_used >= final_bytes_used);

  // We don't keep the trailing '\0' in our output string
  output.append(heap_buffer.get(), size_t(final_bytes_used));
}

} // namespace

std::string stringPrintf(const char* format, ...) {
  va_list ap;
  va_start(ap, format);
  SCOPE_EXIT { va_end(ap); };
  return stringVPrintf(format, ap);
}

std::string stringVPrintf(const char* format, va_list ap) {
  std::string ret;
  stringAppendfImpl(ret, format, ap);
  return ret;
}

// Basic declarations; allow for parameters of strings and string
// pieces to be specified.
std::string& stringAppendf(std::string* output, const char* format, ...) {
  va_list ap;
  va_start(ap, format);
  SCOPE_EXIT { va_end(ap); };
  return stringVAppendf(output, format, ap);
}

std::string& stringVAppendf(
    std::string* output, const char* format, va_list ap) {
  stringAppendfImpl(*output, format, ap);
  return *output;
}

void stringPrintf(std::string* output, const char* format, ...) {
  va_list ap;
  va_start(ap, format);
  SCOPE_EXIT { va_end(ap); };
  return stringVPrintf(output, format, ap);
}

void stringVPrintf(std::string* output, const char* format, va_list ap) {
  output->clear();
  stringAppendfImpl(*output, format, ap);
}

namespace {

struct PrettySuffix {
  const char* suffix;
  double val;
};

const PrettySuffix kPrettyTimeSuffixes[] = {
    {"s ", 1e0L},
    {"ms", 1e-3L},
    {"us", 1e-6L},
    {"ns", 1e-9L},
    {"ps", 1e-12L},
    {"s ", 0},
    {nullptr, 0},
};

const PrettySuffix kPrettyTimeHmsSuffixes[] = {
    {"h ", 60L * 60L},
    {"m ", 60L},
    {"s ", 1e0L},
    {"ms", 1e-3L},
    {"us", 1e-6L},
    {"ns", 1e-9L},
    {"ps", 1e-12L},
    {"s ", 0},
    {nullptr, 0},
};

const PrettySuffix kPrettyBytesMetricSuffixes[] = {
    {"EB", 1e18L},
    {"PB", 1e15L},
    {"TB", 1e12L},
    {"GB", 1e9L},
    {"MB", 1e6L},
    {"kB", 1e3L},
    {"B ", 0L},
    {nullptr, 0},
};

const PrettySuffix kPrettyBytesBinarySuffixes[] = {
    {"EB", int64_t(1) << 60},
    {"PB", int64_t(1) << 50},
    {"TB", int64_t(1) << 40},
    {"GB", int64_t(1) << 30},
    {"MB", int64_t(1) << 20},
    {"kB", int64_t(1) << 10},
    {"B ", 0L},
    {nullptr, 0},
};

const PrettySuffix kPrettyBytesBinaryIECSuffixes[] = {
    {"EiB", int64_t(1) << 60},
    {"PiB", int64_t(1) << 50},
    {"TiB", int64_t(1) << 40},
    {"GiB", int64_t(1) << 30},
    {"MiB", int64_t(1) << 20},
    {"KiB", int64_t(1) << 10},
    {"B  ", 0L},
    {nullptr, 0},
};

const PrettySuffix kPrettyUnitsMetricSuffixes[] = {
    {"qntl", 1e18L},
    {"qdrl", 1e15L},
    {"tril", 1e12L},
    {"bil", 1e9L},
    {"M", 1e6L},
    {"k", 1e3L},
    {" ", 0},
    {nullptr, 0},
};

const PrettySuffix kPrettyUnitsBinarySuffixes[] = {
    {"E", int64_t(1) << 60},
    {"P", int64_t(1) << 50},
    {"T", int64_t(1) << 40},
    {"G", int64_t(1) << 30},
    {"M", int64_t(1) << 20},
    {"k", int64_t(1) << 10},
    {" ", 0},
    {nullptr, 0},
};

const PrettySuffix kPrettyUnitsBinaryIECSuffixes[] = {
    {"Ei", int64_t(1) << 60},
    {"Pi", int64_t(1) << 50},
    {"Ti", int64_t(1) << 40},
    {"Gi", int64_t(1) << 30},
    {"Mi", int64_t(1) << 20},
    {"Ki", int64_t(1) << 10},
    {"  ", 0},
    {nullptr, 0},
};

const PrettySuffix kPrettySISuffixes[] = {
    {"Y", 1e24L},  {"Z", 1e21L},  {"E", 1e18L},  {"P", 1e15L},  {"T", 1e12L},
    {"G", 1e9L},   {"M", 1e6L},   {"k", 1e3L},   {"h", 1e2L},   {"da", 1e1L},
    {"d", 1e-1L},  {"c", 1e-2L},  {"m", 1e-3L},  {"u", 1e-6L},  {"n", 1e-9L},
    {"p", 1e-12L}, {"f", 1e-15L}, {"a", 1e-18L}, {"z", 1e-21L}, {"y", 1e-24L},
    {" ", 0},      {nullptr, 0},
};

const PrettySuffix* const kPrettySuffixes[PRETTY_NUM_TYPES] = {
    kPrettyTimeSuffixes,
    kPrettyTimeHmsSuffixes,
    kPrettyBytesMetricSuffixes,
    kPrettyBytesBinarySuffixes,
    kPrettyBytesBinaryIECSuffixes,
    kPrettyUnitsMetricSuffixes,
    kPrettyUnitsBinarySuffixes,
    kPrettyUnitsBinaryIECSuffixes,
    kPrettySISuffixes,
};

} // namespace

std::string prettyPrint(double val, PrettyType type, bool addSpace) {
  char buf[100];

  // pick the suffixes to use
  assert(type >= 0);
  assert(type < PRETTY_NUM_TYPES);
  const PrettySuffix* suffixes = kPrettySuffixes[type];

  // find the first suffix we're bigger than -- then use it
  double abs_val = fabs(val);
  for (int i = 0; suffixes[i].suffix; ++i) {
    if (abs_val >= suffixes[i].val) {
      snprintf(
          buf,
          sizeof buf,
          "%.4g%s%s",
          (suffixes[i].val ? (val / suffixes[i].val) : val),
          (addSpace ? " " : ""),
          suffixes[i].suffix);
      return std::string(buf);
    }
  }

  // no suffix, we've got a tiny value -- just print it in sci-notation
  snprintf(buf, sizeof buf, "%.4g", val);
  return std::string(buf);
}

// TODO:
// 1) Benchmark & optimize
double prettyToDouble(
    folly::StringPiece* const prettyString, const PrettyType type) {
  auto value = folly::to<double>(prettyString);
  while (!prettyString->empty() && std::isspace(prettyString->front())) {
    prettyString->advance(1); // Skipping spaces between number and suffix
  }
  const PrettySuffix* suffixes = kPrettySuffixes[type];
  int longestPrefixLen = -1;
  int bestPrefixId = -1;
  for (int j = 0; suffixes[j].suffix; ++j) {
    if (suffixes[j].suffix[0] == ' ') { // Checking for " " -> number rule.
      if (longestPrefixLen == -1) {
        longestPrefixLen = 0; // No characters to skip
        bestPrefixId = j;
      }
    } else if (prettyString->startsWith(suffixes[j].suffix)) {
      int suffixLen = int(strlen(suffixes[j].suffix));
      // We are looking for a longest suffix matching prefix of the string
      // after numeric value. We need this in case suffixes have common prefix.
      if (suffixLen > longestPrefixLen) {
        longestPrefixLen = suffixLen;
        bestPrefixId = j;
      }
    }
  }
  if (bestPrefixId == -1) { // No valid suffix rule found
    throw std::invalid_argument(folly::to<std::string>(
        "Unable to parse suffix \"", *prettyString, "\""));
  }
  prettyString->advance(size_t(longestPrefixLen));
  return suffixes[bestPrefixId].val ? value * suffixes[bestPrefixId].val
                                    : value;
}

double prettyToDouble(folly::StringPiece prettyString, const PrettyType type) {
  double result = prettyToDouble(&prettyString, type);
  detail::enforceWhitespace(prettyString);
  return result;
}

std::string hexDump(const void* ptr, size_t size) {
  std::ostringstream os;
  hexDump(ptr, size, std::ostream_iterator<StringPiece>(os, "\n"));
  return os.str();
}

// There are two variants of `strerror_r` function, one returns
// `int`, and another returns `char*`. Selecting proper version using
// preprocessor macros portably is extremely hard.
//
// For example, on Android function signature depends on `__USE_GNU` and
// `__ANDROID_API__` macros (https://git.io/fjBBE).
//
// So we are using C++ overloading trick: we pass a pointer of
// `strerror_r` to `invoke_strerror_r` function, and C++ compiler
// selects proper function.

FOLLY_MAYBE_UNUSED
static std::string invoke_strerror_r(
    int (*strerror_r)(int, char*, size_t), int err, char* buf, size_t buflen) {
  // Using XSI-compatible strerror_r
  int r = strerror_r(err, buf, buflen);

  // OSX/FreeBSD use EINVAL and Linux uses -1 so just check for non-zero
  if (r != 0) {
    return to<std::string>(
        "Unknown error ", err, " (strerror_r failed with error ", errno, ")");
  } else {
    return buf;
  }
}

FOLLY_MAYBE_UNUSED
static std::string invoke_strerror_r(
    char* (*strerror_r)(int, char*, size_t),
    int err,
    char* buf,
    size_t buflen) {
  // Using GNU strerror_r
  return strerror_r(err, buf, buflen);
}

std::string errnoStr(int err) {
  int savedErrno = errno;

  // Ensure that we reset errno upon exit.
  auto guard(makeGuard([&] { errno = savedErrno; }));

  char buf[1024];
  buf[0] = '\0';

  std::string result;

  // https://developer.apple.com/library/mac/documentation/Darwin/Reference/ManPages/man3/strerror_r.3.html
  // http://www.kernel.org/doc/man-pages/online/pages/man3/strerror.3.html
#if defined(_WIN32) && (defined(__MINGW32__) || defined(_MSC_VER))
  // mingw64 has no strerror_r, but Windows has strerror_s, which C11 added
  // as well. So maybe we should use this across all platforms (together
  // with strerrorlen_s). Note strerror_r and _s have swapped args.
  int r = strerror_s(buf, sizeof(buf), err);
  if (r != 0) {
    result = to<std::string>(
        "Unknown error ", err, " (strerror_r failed with error ", errno, ")");
  } else {
    result.assign(buf);
  }
#else
  // Using any strerror_r
  result.assign(invoke_strerror_r(strerror_r, err, buf, sizeof(buf)));
#endif

  return result;
}

namespace {

void toLowerAscii8(char& c) {
  // Branchless tolower, based on the input-rotating trick described
  // at http://www.azillionmonkeys.com/qed/asmexample.html
  //
  // This algorithm depends on an observation: each uppercase
  // ASCII character can be converted to its lowercase equivalent
  // by adding 0x20.

  // Step 1: Clear the high order bit. We'll deal with it in Step 5.
  auto rotated = uint8_t(c & 0x7f);
  // Currently, the value of rotated, as a function of the original c is:
  //   below 'A':   0- 64
  //   'A'-'Z':    65- 90
  //   above 'Z':  91-127

  // Step 2: Add 0x25 (37)
  rotated += 0x25;
  // Now the value of rotated, as a function of the original c is:
  //   below 'A':   37-101
  //   'A'-'Z':    102-127
  //   above 'Z':  128-164

  // Step 3: clear the high order bit
  rotated &= 0x7f;
  //   below 'A':   37-101
  //   'A'-'Z':    102-127
  //   above 'Z':    0- 36

  // Step 4: Add 0x1a (26)
  rotated += 0x1a;
  //   below 'A':   63-127
  //   'A'-'Z':    128-153
  //   above 'Z':   25- 62

  // At this point, note that only the uppercase letters have been
  // transformed into values with the high order bit set (128 and above).

  // Step 5: Shift the high order bit 2 spaces to the right: the spot
  // where the only 1 bit in 0x20 is.  But first, how we ignored the
  // high order bit of the original c in step 1?  If that bit was set,
  // we may have just gotten a false match on a value in the range
  // 128+'A' to 128+'Z'.  To correct this, need to clear the high order
  // bit of rotated if the high order bit of c is set.  Since we don't
  // care about the other bits in rotated, the easiest thing to do
  // is invert all the bits in c and bitwise-and them with rotated.
  rotated &= ~c;
  rotated >>= 2;

  // Step 6: Apply a mask to clear everything except the 0x20 bit
  // in rotated.
  rotated &= 0x20;

  // At this point, rotated is 0x20 if c is 'A'-'Z' and 0x00 otherwise

  // Step 7: Add rotated to c
  c += char(rotated);
}

void toLowerAscii32(uint32_t& c) {
  // Besides being branchless, the algorithm in toLowerAscii8() has another
  // interesting property: None of the addition operations will cause
  // an overflow in the 8-bit value.  So we can pack four 8-bit values
  // into a uint32_t and run each operation on all four values in parallel
  // without having to use any CPU-specific SIMD instructions.
  uint32_t rotated = c & uint32_t(0x7f7f7f7fL);
  rotated += uint32_t(0x25252525L);
  rotated &= uint32_t(0x7f7f7f7fL);
  rotated += uint32_t(0x1a1a1a1aL);

  // Step 5 involves a shift, so some bits will spill over from each
  // 8-bit value into the next.  But that's okay, because they're bits
  // that will be cleared by the mask in step 6 anyway.
  rotated &= ~c;
  rotated >>= 2;
  rotated &= uint32_t(0x20202020L);
  c += rotated;
}

void toLowerAscii64(uint64_t& c) {
  // 64-bit version of toLower32
  uint64_t rotated = c & uint64_t(0x7f7f7f7f7f7f7f7fL);
  rotated += uint64_t(0x2525252525252525L);
  rotated &= uint64_t(0x7f7f7f7f7f7f7f7fL);
  rotated += uint64_t(0x1a1a1a1a1a1a1a1aL);
  rotated &= ~c;
  rotated >>= 2;
  rotated &= uint64_t(0x2020202020202020L);
  c += rotated;
}

} // namespace

void toLowerAscii(char* str, size_t length) {
  static const size_t kAlignMask64 = 7;
  static const size_t kAlignMask32 = 3;

  // Convert a character at a time until we reach an address that
  // is at least 32-bit aligned
  auto n = (size_t)str;
  n &= kAlignMask32;
  n = std::min(n, length);
  size_t offset = 0;
  if (n != 0) {
    n = std::min(4 - n, length);
    do {
      toLowerAscii8(str[offset]);
      offset++;
    } while (offset < n);
  }

  n = (size_t)(str + offset);
  n &= kAlignMask64;
  if ((n != 0) && (offset + 4 <= length)) {
    // The next address is 32-bit aligned but not 64-bit aligned.
    // Convert the next 4 bytes in order to get to the 64-bit aligned
    // part of the input.
    toLowerAscii32(*(uint32_t*)(str + offset));
    offset += 4;
  }

  // Convert 8 characters at a time
  while (offset + 8 <= length) {
    toLowerAscii64(*(uint64_t*)(str + offset));
    offset += 8;
  }

  // Convert 4 characters at a time
  while (offset + 4 <= length) {
    toLowerAscii32(*(uint32_t*)(str + offset));
    offset += 4;
  }

  // Convert any characters remaining after the last 4-byte aligned group
  while (offset < length) {
    toLowerAscii8(str[offset]);
    offset++;
  }
}

namespace detail {

size_t hexDumpLine(
    const void* ptr, size_t offset, size_t size, std::string& line) {
  static char hexValues[] = "0123456789abcdef";
  // Line layout:
  // 8: address
  // 1: space
  // (1+2)*16: hex bytes, each preceded by a space
  // 1: space separating the two halves
  // 3: "  |"
  // 16: characters
  // 1: "|"
  // Total: 78
  line.clear();
  line.reserve(78);
  const uint8_t* p = reinterpret_cast<const uint8_t*>(ptr) + offset;
  size_t n = std::min(size - offset, size_t(16));
  line.push_back(hexValues[(offset >> 28) & 0xf]);
  line.push_back(hexValues[(offset >> 24) & 0xf]);
  line.push_back(hexValues[(offset >> 20) & 0xf]);
  line.push_back(hexValues[(offset >> 16) & 0xf]);
  line.push_back(hexValues[(offset >> 12) & 0xf]);
  line.push_back(hexValues[(offset >> 8) & 0xf]);
  line.push_back(hexValues[(offset >> 4) & 0xf]);
  line.push_back(hexValues[offset & 0xf]);
  line.push_back(' ');

  for (size_t i = 0; i < n; i++) {
    if (i == 8) {
      line.push_back(' ');
    }

    line.push_back(' ');
    line.push_back(hexValues[(p[i] >> 4) & 0xf]);
    line.push_back(hexValues[p[i] & 0xf]);
  }

  // 3 spaces for each byte we're not printing, one separating the halves
  // if necessary
  line.append(3 * (16 - n) + (n <= 8), ' ');
  line.append("  |");

  for (size_t i = 0; i < n; i++) {
    char c = (p[i] >= 32 && p[i] <= 126 ? static_cast<char>(p[i]) : '.');
    line.push_back(c);
  }
  line.append(16 - n, ' ');
  line.push_back('|');
  DCHECK_EQ(line.size(), 78u);

  return n;
}

} // namespace detail

std::string stripLeftMargin(std::string s) {
  std::vector<StringPiece> pieces;
  split("\n", s, pieces);
  auto piecer = range(pieces);

  auto piece = (piecer.end() - 1);
  auto needle = std::find_if(piece->begin(), piece->end(), [](char c) {
    return c != ' ' && c != '\t';
  });
  if (needle == piece->end()) {
    (piecer.end() - 1)->clear();
  }
  piece = piecer.begin();
  needle = std::find_if(piece->begin(), piece->end(), [](char c) {
    return c != ' ' && c != '\t';
  });
  if (needle == piece->end()) {
    piecer.erase(piecer.begin(), piecer.begin() + 1);
  }

  const auto sentinel = std::numeric_limits<size_t>::max();
  auto indent = sentinel;
  size_t max_length = 0;
  for (piece = piecer.begin(); piece != piecer.end(); piece++) {
    needle = std::find_if(piece->begin(), piece->end(), [](char c) {
      return c != ' ' && c != '\t';
    });
    if (needle != piece->end()) {
      indent = std::min<size_t>(indent, size_t(needle - piece->begin()));
    } else {
      max_length = std::max<size_t>(piece->size(), max_length);
    }
  }
  indent = indent == sentinel ? max_length : indent;
  for (piece = piecer.begin(); piece != piecer.end(); piece++) {
    if (piece->size() < indent) {
      piece->clear();
    } else {
      piece->erase(piece->begin(), piece->begin() + indent);
    }
  }
  return join("\n", piecer);
}

} // namespace folly

#ifdef FOLLY_DEFINED_DMGL
#undef FOLLY_DEFINED_DMGL
#undef DMGL_NO_OPTS
#undef DMGL_PARAMS
#undef DMGL_ANSI
#undef DMGL_JAVA
#undef DMGL_VERBOSE
#undef DMGL_TYPES
#undef DMGL_RET_POSTFIX
#endif