bclamp.d

   1 /* Invisible Vector Library
   2  * coded by Ketmar // Invisible Vector <ketmar@ketmar.no-ip.org>
   3  * Understanding is not required. Only obedience.
   4  *
   5  * This program is free software: you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation, version 3 of the License ONLY.
   8  *
   9  * This program is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  16  */
  17 // just `clampToByte()`, so i can easily find and copypaste it
  18 module iv.bclamp /*is aliced*/;
  19
  20
  21 // this is actually branch-less for ints on x86, and even for longs on x86_64
  22 ubyte clampToByte(T) (T n) pure nothrow @safe @nogc if (__traits(isIntegral, T)) {
  23   pragma(inline, true);
  24   static if (T.sizeof == 2 || T.sizeof == 4) {
  25     static if (__traits(isUnsigned, T)) {
  26       return cast(ubyte)(n&0xff|(255-((-cast(int)(n < 256))>>24)));
  27     } else {
  28       n &= -cast(int)(n >= 0);
  29       return cast(ubyte)(n|((255-cast(int)n)>>31));
  30     }
  31   } else static if (T.sizeof == 1) {
  32     static assert(__traits(isUnsigned, T), "clampToByte: signed byte? no, really?");
  33     return cast(ubyte)n;
  34   } else static if (T.sizeof == 8) {
  35     static if (__traits(isUnsigned, T)) {
  36       return cast(ubyte)(n&0xff|(255-((-cast(long)(n < 256))>>56)));
  37     } else {
  38       n &= -cast(long)(n >= 0);
  39       return cast(ubyte)(n|((255-cast(long)n)>>63));
  40     }
  41   } else {
  42     static assert(false, "clampToByte: integer too big");
  43   }
  44 }
  45
  46
  47 unittest {
  48   static assert(clampToByte(666) == 255);
  49   static assert(clampToByte(-666) == 0);
  50   static assert(clampToByte(250) == 250);
  51   static assert(clampToByte(-250) == 0);
  52   static assert(clampToByte(cast(uint)250) == 250);
  53   static assert(clampToByte(cast(uint)1000) == 255);
  54   static assert(clampToByte(cast(uint)0xfffffff0) == 255);
  55   static assert(clampToByte(false) == 0);
  56   static assert(clampToByte(true) == 1);
  57   static assert(clampToByte('A') == 65);
  58
  59   static assert(clampToByte(666L) == 255);
  60   static assert(clampToByte(-666L) == 0);
  61   static assert(clampToByte(250L) == 250);
  62   static assert(clampToByte(-250L) == 0);
  63   static assert(clampToByte(-666UL) == 255);
  64 }