CommandStation-EX/KeywordHasher.h

/*
 *  © 2024 Vincent Hamp and Chris Harlow
 *  All rights reserved.
 *  
 *  This file is part of CommandStation-EX
 *
 *  This is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  It is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with CommandStation.  If not, see <https://www.gnu.org/licenses/>.
 */


/* Reader be aware: 
 This function implements the _hk data type so that a string keyword
 is hashed to the same value as the DCCEXParser uses to hash incoming 
 keywords. 
 Thus  "MAIN"_hk  generates exactly the same run time vakue 
 as   const int16_t HASH_KEYWORD_MAIN=11339  
*/
#ifndef KeywordHasher_h
#define KeywordHasher_h

#include <Arduino.h>
constexpr uint16_t CompiletimeKeywordHasher(const char *  sv, uint16_t running=0) {
    return (*sv==0) ? running : CompiletimeKeywordHasher(sv+1,
          (*sv >= '0' && *sv <= '9') 
            ? (10*running+*sv-'0')  // Numeric hash  
            : ((running << 5) + running) ^ *sv
            );  // 
}

constexpr int16_t operator""_hk(const char * keyword, size_t len) 
{
    return (int16_t) CompiletimeKeywordHasher(keyword,len*0);
}

/* Some historical values for testing:
const int16_t HASH_KEYWORD_MAIN = 11339;
const int16_t HASH_KEYWORD_SLOW = -17209;
const int16_t HASH_KEYWORD_SPEED28 = -17064;
const int16_t HASH_KEYWORD_SPEED128 = 25816;
*/

static_assert("MAIN"_hk == 11339,"Keyword hasher error");
static_assert("SLOW"_hk == -17209,"Keyword hasher error");
static_assert("SPEED28"_hk == -17064,"Keyword hasher error");
static_assert("SPEED128"_hk == 25816,"Keyword hasher error");

// Compile time converter from "abcd"_s7  to the 7 segment nearest equivalent

constexpr uint8_t seg7Digits[]={
      0b00111111,0b00000110,0b01011011,0b01001111, // 0..3
      0b01100110,0b01101101,0b01111101,0b00000111, // 4..7
      0b01111111,0b01101111 // 8..9
    };
    
constexpr uint8_t seg7Letters[]={
        0b01110111,0b01111100,0b00111001,0b01011110, // ABCD
        0b01111001,0b01110001,0b00111101,0b01110110, // EFGH 
        0b00000100,0b00011110,0b01110010,0b00111000,  //IJKL
        0b01010101,0b01010100,0b01011100,0b01110011, // MNOP
        0b10111111,0b01010000,0b01101101,0b01111000, // QRST
        0b00111110,0b00011100,0b01101010,0b01001001,  //UVWX
        0b01100110,0b01011011  //YZ
    };
constexpr uint8_t seg7Space=0b00000000;
constexpr uint8_t seg7Minus=0b01000000;
constexpr uint8_t seg7Equals=0b01001000;
    

constexpr uint32_t CompiletimeSeg7(const char *  sv, uint32_t running, size_t rlen) {
    return (*sv==0 || rlen==0) ? running << (8*rlen) : CompiletimeSeg7(sv+1,
          (*sv >= '0' && *sv <= '9') ? (running<<8) | seg7Digits[*sv-'0'] : 
          (*sv >= 'A' && *sv <= 'Z') ? (running<<8) | seg7Letters[*sv-'A'] : 
          (*sv >= 'a' && *sv <= 'z') ? (running<<8) | seg7Letters[*sv-'a'] : 
          (*sv == '-') ? (running<<8) | seg7Minus : 
          (*sv == '=') ? (running<<8) | seg7Equals : 
                         (running<<8) | seg7Space,
          rlen-1               
        );  // 
}

constexpr uint32_t operator""_s7(const char * keyword, size_t len) 
{
    return  CompiletimeSeg7(keyword,0*len,4);
}
#endif