itoa_ljust.c

//=== itoa_ljust.cpp - Fast integer to ascii conversion           --*- C++ -*-//
//
// Substantially simplified (and slightly faster) version
// based on the following functions in Google's protocol buffers:
//
//    FastInt32ToBufferLeft()
//    FastUInt32ToBufferLeft()
//    FastInt64ToBufferLeft()
//    FastUInt64ToBufferLeft()
//
// Differences:
//    1) Greatly simplified
//    2) Avoids GOTO statements - uses "switch" instead and relies on
//       compiler constant folding and propagation for high performance
//    3) Avoids unary minus of signed types - undefined behavior if value
//       is INT_MIN in platforms using two's complement representation
//    4) Uses memcpy to store 2 digits at a time - lets the compiler
//       generate a 2-byte load/store in platforms that support
//       unaligned access, this is faster (and less code) than explicitly
//       loading and storing each byte
//
// Copyright (c) 2016 Arturo Martin-de-Nicolas
// arturomdn@gmail.com
// https://github.com/amdn/itoa_ljust/
//
// Released under the BSD 3-Clause License, see Google's original copyright
// and license below.
//===----------------------------------------------------------------------===//

// Protocol Buffers - Google's data interchange format
// Copyright 2008 Google Inc.  All rights reserved.
// https://developers.google.com/protocol-buffers/
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
//     * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
//     * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
//===----------------------------------------------------------------------===//

#include "itoa_ljust.h"
#include <string.h>

static const char lut[201] = "0001020304050607080910111213141516171819"
                             "2021222324252627282930313233343536373839"
                             "4041424344454647484950515253545556575859"
                             "6061626364656667686970717273747576777879"
                             "8081828384858687888990919293949596979899";

#define dd(u) ((const uint16_t)(lut[u]))

static inline char *out2(const int d, char *p) {
  memcpy(p, &((uint16_t *)lut)[d], 2);
  return p + 2;
}

static inline char *out1(const char in, char *p) {
  memcpy(p, &in, 1);
  return p + 1;
}

static inline int digits(uint32_t u, unsigned k, int *d, char **p, int n) {
  if (u < k * 10) {
    *d = u / k;
    *p = out1('0' + *d, *p);
    --n;
  }
  return n;
}

static inline char *itoa(uint32_t u, char *p, int d, int n) {
  switch (n) {
  case 10:
    d = u / 100000000;
    p = out2(d, p);
  case 9:
    u -= d * 100000000;
  case 8:
    d = u / 1000000;
    p = out2(d, p);
  case 7:
    u -= d * 1000000;
  case 6:
    d = u / 10000;
    p = out2(d, p);
  case 5:
    u -= d * 10000;
  case 4:
    d = u / 100;
    p = out2(d, p);
  case 3:
    u -= d * 100;
  case 2:
    d = u / 1;
    p = out2(d, p);
  case 1:;
  }
  *p = '\0';
  return p;
}

char *itoa_u32(uint32_t u, char *p) {
  int d = 0, n;
  if (u >= 100000000)
    n = digits(u, 100000000, &d, &p, 10);
  else if (u < 100)
    n = digits(u, 1, &d, &p, 2);
  else if (u < 10000)
    n = digits(u, 100, &d, &p, 4);
  else if (u < 1000000)
    n = digits(u, 10000, &d, &p, 6);
  else
    n = digits(u, 1000000, &d, &p, 8);
  return itoa(u, p, d, n);
}

char *itoa_32(int32_t i, char *p) {
  uint32_t u = i;
  if (i < 0) {
    *p++ = '-';
    u = -u;
  }
  return itoa_u32(u, p);
}

char *itoa_u64(uint64_t u, char *p) {
  int d;

  uint32_t lower = (uint32_t)u;
  if (lower == u)
    return itoa_u32(lower, p);

  uint64_t upper = u / 1000000000;
  p = itoa_u64(upper, p);
  lower = u - (upper * 1000000000);
  d = lower / 100000000;
  p = out1('0' + d, p);
  return itoa(lower, p, d, 9);
}

char *itoa_64(int64_t i, char *p) {
  uint64_t u = i;
  if (i < 0) {
    *p++ = '-';
    u = -u;
  }
  return itoa_u64(u, p);
}