hextoint

Parse.cpp

// Does not reject invalid data. define NO_OVERFLOW to avoid values
// larger than 15, but it will still accept invalid characters.

// MSN(x) = Most-significant nibble
// LSN(x) = Least-significant nibble
// SHL(x, y) = Shift left
// SHR(x, y) = Shift right

// MSN(Digits) = 0011
// MSN(Upper) = 0100
// MSN(Lower) = 0110

// LSN(0) = 0000, LSN(9) = 1001
// LSN(a|A) = 0001, LSN(f|F) = 0110

uint8_t hextoint(uint8_t c)
{
  // =1 for Upper/Lower, =0 for Digit
  // SHR(a, 6) = SHR(0110 0001, 6) = 0000 0001
  uint8_t ms = (c >> 6);
#ifdef NO_OVERFLOW
  ms &= 0b0001; // MSB may be set
#endif

  // =9 for Upper/Lower, =0 for Digit
  // LSN(Upper/Lower) is one too large, otherwise we'd use 10 (a/A = 10)
  // SHL(0001, 3) | 0001 = 1000 | 0001 = 1001
  uint8_t nine = (ms << 3) | ms;

  // Extract LSN, which is still 1 too large for Alpha/alpha
  c &= 0xF;

#ifdef NO_OVERFLOW
  c ^=
    // for g, c = 0111 = 7
    //  SHR(0111, 1) = 0011
    //  SHL(0111, 1) = 1110
    // 0111 AND 0010 = 0010
    //                 ----
    //           AND = 0010
    //         XOR c = 0101 = 5    
    ((c >> 1) & (c << 1) & (c & 0x2))

    // for h, c = 1000 (and nine = 1001) = 17
    //    SHL(ms, 3) = 1000
    //         AND c = 1000
    //         XOR c = 0000
    | ((ms << 3) & c);
#endif

  return c + nine;
}

uint8_t hextoint(uint8_t c1, uint8_t c2)
{
  return (hextoint(c1) << 4) | hextoint(c2);
}

MIT, obviously.

Copyright 2018 Jonathan Dickinson

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

uint8_t hextoint(uint8_t c)
{
// =1 cho Trên/Dưới, =0 cho Chữ số
// SHR(a, 6) = SHR(0110 0001, 6) = 0000 0001
uint8_t ms = (c >> 6);
#ifdef KHÔNG_TRÀN
ms &= 0b0001; // MSB có thể được đặt
#kết thúc

// =9 cho Trên/Dưới, =0 cho Chữ số
// LSN(Upper/Lower) là một cái quá lớn, nếu không chúng tôi sẽ sử dụng 10 (a/A = 10)
// SHL(0001, 3) | 0001 = 1000 | 0001 = 1001
uint8_t chín = (ms << 3) | ms;

// Trích xuất LSN, vẫn còn 1 quá lớn đối với Alpha/alpha
c &= 0xF;