hphp/util/conv-10.cpp

   1 /*
   2    +----------------------------------------------------------------------+
   3    | HipHop for PHP                                                       |
   4    +----------------------------------------------------------------------+
   5    | Copyright (c) 2010-present Facebook, Inc. (http://www.facebook.com)  |
   6    +----------------------------------------------------------------------+
   7    | This source file is subject to version 3.01 of the PHP license,      |
   8    | that is bundled with this package in the file LICENSE, and is        |
   9    | available through the world-wide-web at the following url:           |
  10    | http://www.php.net/license/3_01.txt                                  |
  11    | If you did not receive a copy of the PHP license and are unable to   |
  12    | obtain it through the world-wide-web, please send a note to          |
  13    | license@php.net so we can mail you a copy immediately.               |
  14    +----------------------------------------------------------------------+
  15 */
  16
  17 #include "hphp/util/conv-10.h"
  18
  19 namespace HPHP {
  20
  21 folly::StringPiece conv_10(int64_t num, char* buf_end) {
  22   auto p = buf_end;
  23   uint64_t magnitude;
  24
  25   /*
  26    * On a 2's complement machine, negating the most negative integer
  27    * results in a number that cannot be represented as a signed integer.
  28    * Here is what we do to obtain the number's magnitude:
  29    *      a. add 1 to the number
  30    *      b. negate it (becomes positive)
  31    *      c. convert it to unsigned
  32    *      d. add 1
  33    */
  34   if (num < 0) {
  35     magnitude = static_cast<uint64_t>(-(num + 1)) + 1;
  36   } else {
  37     magnitude = static_cast<uint64_t>(num);
  38   }
  39
  40   /*
  41    * We use a do-while loop so that we write at least 1 digit
  42    */
  43   do {
  44     auto const q = magnitude / 10;
  45     auto const r = static_cast<uint32_t>(magnitude % 10);
  46     *--p = r + '0';
  47     magnitude = q;
  48   } while (magnitude);
  49
  50   if (num < 0) *--p = '-';
  51   return folly::StringPiece{p, static_cast<size_t>(buf_end - p)};
  52 }
  53
  54 }