bit reversing by lookup table instead of function; it's faster

diff --git a/lcd.c b/lcd.c
index a7cf98ffd19f21e4bc4093136bbe14b5ee2227ca..786359779878803bb7ecaa9cd113b44775ee0ad5 100644 (file)
--- a/lcd.c
+++ b/lcd.c
@@ -332,7 +332,7 @@ void lcd_write ( // write single byte to LCD
        LCD_D__PM = 0x00; //data output
        
        if (chip == LCD_LEFT) //reverse bits for left chip
-               d = reverse_bits(data);
+               d = REVERSE_BITS[data];
        else
                d = data;
        

diff --git a/main.c b/main.c
index 658e5b4e7cc76614b1f4d85968275db66b578de7..a1c34fb5643492854f4796c890a29a7cf1c0988b 100644 (file)
--- a/main.c
+++ b/main.c
@@ -18,6 +18,25 @@ THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
 #include "ctrl.h"
 #include "fs.h"
 
+const uint8_t REVERSE_BITS[256] = { // reverse order of bits in a byte
+       0x00, 0x80, 0x40, 0xc0, 0x20, 0xa0, 0x60, 0xe0, 0x10, 0x90, 0x50, 0xd0, 0x30, 0xb0, 0x70, 0xf0,
+       0x08, 0x88, 0x48, 0xc8, 0x28, 0xa8, 0x68, 0xe8, 0x18, 0x98, 0x58, 0xd8, 0x38, 0xb8, 0x78, 0xf8,
+       0x04, 0x84, 0x44, 0xc4, 0x24, 0xa4, 0x64, 0xe4, 0x14, 0x94, 0x54, 0xd4, 0x34, 0xb4, 0x74, 0xf4,
+       0x0c, 0x8c, 0x4c, 0xcc, 0x2c, 0xac, 0x6c, 0xec, 0x1c, 0x9c, 0x5c, 0xdc, 0x3c, 0xbc, 0x7c, 0xfc,
+       0x02, 0x82, 0x42, 0xc2, 0x22, 0xa2, 0x62, 0xe2, 0x12, 0x92, 0x52, 0xd2, 0x32, 0xb2, 0x72, 0xf2,
+       0x0a, 0x8a, 0x4a, 0xca, 0x2a, 0xaa, 0x6a, 0xea, 0x1a, 0x9a, 0x5a, 0xda, 0x3a, 0xba, 0x7a, 0xfa,
+       0x06, 0x86, 0x46, 0xc6, 0x26, 0xa6, 0x66, 0xe6, 0x16, 0x96, 0x56, 0xd6, 0x36, 0xb6, 0x76, 0xf6,
+       0x0e, 0x8e, 0x4e, 0xce, 0x2e, 0xae, 0x6e, 0xee, 0x1e, 0x9e, 0x5e, 0xde, 0x3e, 0xbe, 0x7e, 0xfe,
+       0x01, 0x81, 0x41, 0xc1, 0x21, 0xa1, 0x61, 0xe1, 0x11, 0x91, 0x51, 0xd1, 0x31, 0xb1, 0x71, 0xf1,
+       0x09, 0x89, 0x49, 0xc9, 0x29, 0xa9, 0x69, 0xe9, 0x19, 0x99, 0x59, 0xd9, 0x39, 0xb9, 0x79, 0xf9,
+       0x05, 0x85, 0x45, 0xc5, 0x25, 0xa5, 0x65, 0xe5, 0x15, 0x95, 0x55, 0xd5, 0x35, 0xb5, 0x75, 0xf5,
+       0x0d, 0x8d, 0x4d, 0xcd, 0x2d, 0xad, 0x6d, 0xed, 0x1d, 0x9d, 0x5d, 0xdd, 0x3d, 0xbd, 0x7d, 0xfd,
+       0x03, 0x83, 0x43, 0xc3, 0x23, 0xa3, 0x63, 0xe3, 0x13, 0x93, 0x53, 0xd3, 0x33, 0xb3, 0x73, 0xf3,
+       0x0b, 0x8b, 0x4b, 0xcb, 0x2b, 0xab, 0x6b, 0xeb, 0x1b, 0x9b, 0x5b, 0xdb, 0x3b, 0xbb, 0x7b, 0xfb,
+       0x07, 0x87, 0x47, 0xc7, 0x27, 0xa7, 0x67, 0xe7, 0x17, 0x97, 0x57, 0xd7, 0x37, 0xb7, 0x77, 0xf7,
+       0x0f, 0x8f, 0x4f, 0xcf, 0x2f, 0xaf, 0x6f, 0xef, 0x1f, 0x9f, 0x5f, 0xdf, 0x3f, 0xbf, 0x7f, 0xff
+};
+
 volatile uint32_t main_timer = 0;
 
 inline void int_main_timer (void)
@@ -86,35 +105,6 @@ void main (void)
        }
 }
 
-uint8_t reverse_bits (uint8_t in) // reverse order of bits in a byte
-{
-       uint8_t out = 0;
-       
-       out |= in & 0x01;
-       out <<= 1;
-       in >>= 1;
-       out |= in & 0x01;
-       out <<= 1;
-       in >>= 1;
-       out |= in & 0x01;
-       out <<= 1;
-       in >>= 1;
-       out |= in & 0x01;
-       out <<= 1;
-       in >>= 1;
-       out |= in & 0x01;
-       out <<= 1;
-       in >>= 1;
-       out |= in & 0x01;
-       out <<= 1;
-       in >>= 1;
-       out |= in & 0x01;
-       out <<= 1;
-       in >>= 1;
-       out |= in & 0x01;
-       return out;
-}
-
 uint8_t make_dec_string ( // create decimal text representation of number
        uint8_t * const string,
        uint32_t value,

diff --git a/main.h b/main.h
index fb6247c14f914755ca85ce477a946b6b2abd7436..0cade128f9d11ec194a0340d85e538507356bd7a 100644 (file)
--- a/main.h
+++ b/main.h
@@ -1,5 +1,5 @@
 /*
-Copyright 2021, 2022 Balthasar Szczepański
+Copyright 2021, 2022, 2025 Balthasar Szczepański
 
 Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:
 
@@ -18,7 +18,6 @@ inline void    int_main_timer (void) LOWTEXT; // handle timer every 1ms
        /* ! remember to keep reset_program.asm in agreement with main() definition */
        // int     main (int argc, char ** argv);
        void    main (void);
-       uint8_t reverse_bits (uint8_t in);    // reverse order of bits in a byte
 
 uint8_t make_dec_string ( // create decimal text representation of number
        uint8_t * const string, // address where to create string
@@ -34,4 +33,5 @@ uint8_t make_hex_string ( // create hexadecimal text representation of number
        uint8_t uppercase // bool, 0xABCDEF, or 0xabcdef?
 ); // return actual number of digits
 
-extern volatile uint32_t main_timer; // milliseconds since start
+extern const    uint8_t  REVERSE_BITS[256]; // reverse order of bits in a byte
+extern volatile uint32_t main_timer;        // milliseconds since start