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Reynard

Shifting By Multiples Of 8

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The compiler does not recognise that right shifting by 24 is a multiple of 8 bits.

 

#include <system.h>

unsigned long	mylong;
unsigned char	mychars[5];

void main(void) {

mylong = 0x12345678;
0003  3078	  MOVLW 0x78
0004  1283	  BCF STATUS, RP0
0005  1303	  BCF STATUS, RP1
0006  00A5	  MOVWF gbl_mylong
0007  3056	  MOVLW 0x56
0008  00A6	  MOVWF gbl_mylong+D'1'
0009  3034	  MOVLW 0x34
000A  00A7	  MOVWF gbl_mylong+D'2'
000B  3012	  MOVLW 0x12
000C  00A8	  MOVWF gbl_mylong+D'3'


mychars[0] = (unsigned char)(mylong >> 0);
000D  0825	  MOVF gbl_mylong, W
000E  00A0	  MOVWF gbl_mychars

mychars[1] = (unsigned char)(mylong >> 8);
000F  0826	  MOVF gbl_mylong+D'1', W
0010  00A1	  MOVWF gbl_mychars+D'1'

mychars[2] = (unsigned char)(mylong >> 16);
0011  0827	  MOVF gbl_mylong+D'2', W
0012  00A2	  MOVWF gbl_mychars+D'2'

mychars[2] = (unsigned char)(mylong >> 24);
0013  0825	  MOVF gbl_mylong, W
0014  00A9	  MOVWF CompTempVar499
0015  0826	  MOVF gbl_mylong+D'1', W
0016  00AA	  MOVWF CompTempVar500
0017  0827	  MOVF gbl_mylong+D'2', W
0018  00AB	  MOVWF CompTempVar501
0019  0828	  MOVF gbl_mylong+D'3', W
001A  00AC	  MOVWF CompTempVar502
001B  1003	  BCF STATUS,C
001C  0CAC	  RRF CompTempVar502, F
001D  0CAB	  RRF CompTempVar501, F
001E  0CAA	  RRF CompTempVar500, F
001F  0CA9	  RRF CompTempVar499, F
0020  1003	  BCF STATUS,C
0021  0CAC	  RRF CompTempVar502, F
0022  0CAB	  RRF CompTempVar501, F
0023  0CAA	  RRF CompTempVar500, F
0024  0CA9	  RRF CompTempVar499, F
0025  1003	  BCF STATUS,C
0026  0CAC	  RRF CompTempVar502, F
0027  0CAB	  RRF CompTempVar501, F
0028  0CAA	  RRF CompTempVar500, F
0029  0CA9	  RRF CompTempVar499, F
002A  1003	  BCF STATUS,C
002B  0CAC	  RRF CompTempVar502, F
002C  0CAB	  RRF CompTempVar501, F
002D  0CAA	  RRF CompTempVar500, F
002E  0CA9	  RRF CompTempVar499, F
002F  1003	  BCF STATUS,C
0030  0CAC	  RRF CompTempVar502, F
0031  0CAB	  RRF CompTempVar501, F
0032  0CAA	  RRF CompTempVar500, F
0033  0CA9	  RRF CompTempVar499, F
0034  1003	  BCF STATUS,C
0035  0CAC	  RRF CompTempVar502, F
0036  0CAB	  RRF CompTempVar501, F
0037  0CAA	  RRF CompTempVar500, F
0038  0CA9	  RRF CompTempVar499, F
0039  1003	  BCF STATUS,C
003A  0CAC	  RRF CompTempVar502, F
003B  0CAB	  RRF CompTempVar501, F
003C  0CAA	  RRF CompTempVar500, F
003D  0CA9	  RRF CompTempVar499, F
003E  1003	  BCF STATUS,C
003F  0CAC	  RRF CompTempVar502, F
0040  0CAB	  RRF CompTempVar501, F
0041  0CAA	  RRF CompTempVar500, F
0042  0CA9	  RRF CompTempVar499, F
0043  1003	  BCF STATUS,C
0044  0CAC	  RRF CompTempVar502, F
0045  0CAB	  RRF CompTempVar501, F
0046  0CAA	  RRF CompTempVar500, F
0047  0CA9	  RRF CompTempVar499, F
0048  1003	  BCF STATUS,C
0049  0CAC	  RRF CompTempVar502, F
004A  0CAB	  RRF CompTempVar501, F
004B  0CAA	  RRF CompTempVar500, F
004C  0CA9	  RRF CompTempVar499, F
004D  1003	  BCF STATUS,C
004E  0CAC	  RRF CompTempVar502, F
004F  0CAB	  RRF CompTempVar501, F
0050  0CAA	  RRF CompTempVar500, F
0051  0CA9	  RRF CompTempVar499, F
0052  1003	  BCF STATUS,C
0053  0CAC	  RRF CompTempVar502, F
0054  0CAB	  RRF CompTempVar501, F
0055  0CAA	  RRF CompTempVar500, F
0056  0CA9	  RRF CompTempVar499, F
0057  1003	  BCF STATUS,C
0058  0CAC	  RRF CompTempVar502, F
0059  0CAB	  RRF CompTempVar501, F
005A  0CAA	  RRF CompTempVar500, F
005B  0CA9	  RRF CompTempVar499, F
005C  1003	  BCF STATUS,C
005D  0CAC	  RRF CompTempVar502, F
005E  0CAB	  RRF CompTempVar501, F
005F  0CAA	  RRF CompTempVar500, F
0060  0CA9	  RRF CompTempVar499, F
0061  1003	  BCF STATUS,C
0062  0CAC	  RRF CompTempVar502, F
0063  0CAB	  RRF CompTempVar501, F
0064  0CAA	  RRF CompTempVar500, F
0065  0CA9	  RRF CompTempVar499, F
0066  1003	  BCF STATUS,C
0067  0CAC	  RRF CompTempVar502, F
0068  0CAB	  RRF CompTempVar501, F
0069  0CAA	  RRF CompTempVar500, F
006A  0CA9	  RRF CompTempVar499, F
006B  1003	  BCF STATUS,C
006C  0CAC	  RRF CompTempVar502, F
006D  0CAB	  RRF CompTempVar501, F
006E  0CAA	  RRF CompTempVar500, F
006F  0CA9	  RRF CompTempVar499, F
0070  1003	  BCF STATUS,C
0071  0CAC	  RRF CompTempVar502, F
0072  0CAB	  RRF CompTempVar501, F
0073  0CAA	  RRF CompTempVar500, F
0074  0CA9	  RRF CompTempVar499, F
0075  1003	  BCF STATUS,C
0076  0CAC	  RRF CompTempVar502, F
0077  0CAB	  RRF CompTempVar501, F
0078  0CAA	  RRF CompTempVar500, F
0079  0CA9	  RRF CompTempVar499, F
007A  1003	  BCF STATUS,C
007B  0CAC	  RRF CompTempVar502, F
007C  0CAB	  RRF CompTempVar501, F
007D  0CAA	  RRF CompTempVar500, F
007E  0CA9	  RRF CompTempVar499, F
007F  1003	  BCF STATUS,C
0080  0CAC	  RRF CompTempVar502, F
0081  0CAB	  RRF CompTempVar501, F
0082  0CAA	  RRF CompTempVar500, F
0083  0CA9	  RRF CompTempVar499, F
0084  1003	  BCF STATUS,C
0085  0CAC	  RRF CompTempVar502, F
0086  0CAB	  RRF CompTempVar501, F
0087  0CAA	  RRF CompTempVar500, F
0088  0CA9	  RRF CompTempVar499, F
0089  1003	  BCF STATUS,C
008A  0CAC	  RRF CompTempVar502, F
008B  0CAB	  RRF CompTempVar501, F
008C  0CAA	  RRF CompTempVar500, F
008D  0CA9	  RRF CompTempVar499, F
008E  1003	  BCF STATUS,C
008F  0CAC	  RRF CompTempVar502, F
0090  0CAB	  RRF CompTempVar501, F
0091  0CAA	  RRF CompTempVar500, F
0092  0C29	  RRF CompTempVar499, W
0093  00A2	  MOVWF gbl_mychars+D'2'

mychars[5] = (unsigned char)(mylong >> 32);
0094  3000	  MOVLW 0x00
0095  01A5	  CLRF gbl_mychars+D'5'

}
0096  0008	  RETURN

 

The above code snippet shows shifting by 8, 16 and 32 is handles OK (32 has a redundant instruction though).

Perhaps a loop could be considered for shifts greater than say 8 to produce more compact code with a little loss of speed.

 

Creating a union of a long and char[4] is a workaround to all those shifts to get access to the individual bytes of the long.

 

Cheers

 

Reynard

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