Quickest way to get highest set bit on port in to a variable?

**Tabsoft** · - 8th March 2015, 22:57

Short of resorting to inline ASM and potentially having to deal with bank issues, etc., I put together the suggestions here on this thread and ran the execution tests.
I captured the results in the table below.

Name: BitTestTable.png
Views: 1049
Size: 14.2 KB

Name: BitTestTable.png
Views: 1049
Size: 14.2 KB

Here is the code that I used to test with.

Code:

'****************************************************************
'*  Name    : NCDTest.pbp                                       *
'*  Author  : TABSoft                                           *
'*  Notice  : Copyright (c) 2015 TABSoft                        *
'*          : All Rights Reserved                               *
'*  Date    : 3/3/2015                                          *
'*  Version : 1.0                                               *
'*  Notes   :                                                   *
'*          :                                                   *
'****************************************************************

'*****PIC MCU Configuration Fuses (MPASM)*****
#IF __PROCESSOR__ = "18F4620"
    #CONFIG
        CONFIG OSC = ECIO6            ; EC oscillator, port function on RA6
        ;CONFIG OSC = INTIO67	      ; Internal oscillator block, port function on RA6 and RA7
        ;CONFIG  WDT = OFF             ; WDT disabled (control is placed on the SWDTEN bit)
        CONFIG  FCMEN = OFF           ; Fail-Safe Clock Monitor disabled
        CONFIG  IESO = OFF            ; Oscillator Switchover mode disabled
        CONFIG  PWRT = OFF            ; PWRT disabled
        CONFIG  BOREN = SBORDIS       ; Brown-out Reset enabled in hardware only (SBOREN is disabled)
        CONFIG  BORV = 3              ; Minimum setting
        CONFIG  WDT = ON              ; WDT enabled
        CONFIG  WDTPS = 512           ; 1:512
        CONFIG  CCP2MX = PORTC        ; CCP2 input/output is multiplexed with RC1
        CONFIG  PBADEN = OFF          ; PORTB<4:0> pins are configured as digital I/O on Reset
        CONFIG  LPT1OSC = OFF         ; Timer1 configured for higher power operation
        CONFIG  MCLRE = ON            ; MCLR pin enabled; RE3 input pin disabled
        CONFIG  STVREN = ON           ; Stack full/underflow will cause Reset
        CONFIG  LVP = OFF             ; Single-Supply ICSP disabled
        CONFIG  XINST = OFF           ; Instruction set extension and Indexed Addressing mode disabled (Legacy mode)
        CONFIG  DEBUG = OFF           ; Background debugger disabled, RB6 and RB7 configured as general purpose I/O pins
        CONFIG  CP0 = OFF             ; Block 0 (000800-003FFFh) not code-protected
        CONFIG  CP1 = OFF             ; Block 1 (004000-007FFFh) not code-protected
        CONFIG  CP2 = OFF             ; Block 2 (008000-00BFFFh) not code-protected
        CONFIG  CP3 = OFF             ; Block 3 (00C000-00FFFFh) not code-protected
        CONFIG  CPB = OFF             ; Boot block (000000-0007FFh) not code-protected
        CONFIG  CPD = OFF             ; Data EEPROM not code-protected
        CONFIG  WRT0 = OFF            ; Block 0 (000800-003FFFh) not write-protected
        CONFIG  WRT1 = OFF            ; Block 1 (004000-007FFFh) not write-protected
        CONFIG  WRT2 = OFF            ; Block 2 (008000-00BFFFh) not write-protected
        CONFIG  WRT3 = OFF            ; Block 3 (00C000-00FFFFh) not write-protected
        CONFIG  WRTC = OFF            ; Configuration registers (300000-3000FFh) not write-protected
        CONFIG  WRTB = OFF            ; Boot Block (000000-0007FFh) not write-protected
        CONFIG  WRTD = OFF            ; Data EEPROM not write-protected
        CONFIG  EBTR0 = OFF           ; Block 0 (000800-003FFFh) not protected from table reads executed in other blocks
        CONFIG  EBTR1 = OFF           ; Block 1 (004000-007FFFh) not protected from table reads executed in other blocks
        CONFIG  EBTR2 = OFF           ; Block 2 (008000-00BFFFh) not protected from table reads executed in other blocks
        CONFIG  EBTR3 = OFF           ; Block 3 (00C000-00FFFFh) not protected from table reads executed in other blocks
        CONFIG  EBTRB = OFF           ; Boot Block (000000-0007FFh) not protected from table reads executed in other blocks

    #ENDCONFIG
#else
    #ERROR "This program requires a PIC 18F4620 MCU"
#endif

OSCCON = $60  ' Set PIC to 4Mhz & ECIO Clock Mode

 DEFINE OSC 4
 ADCON0.0 = 0  ' A/D Converter module is disabled   
   ADCON1 = $0F  ' %0000 1111 AN2=VSS, AN3=VDD, AN12-0 = Digital 
   ADCON2 = $00  ' %0000 0000
    TRISB = %11111111 ' Set PORTB as input
INTCON2.7 = 0 ' Enable PORTB pullups
    TRISC = TRISC & %11011111   ' Set PORTC pin directions (pin5 output to RTC VCC2)

i var byte
mybyte var byte
mystatus var byte
workword var word
workbyte var workword.byte0 ' 1st byte
bitcarry var workword.8 ' 9th bit
bitcount var byte
bytArray var byte[9]

bytArray[0] = 0
bytArray[1] = 1
bytArray[2] = 2
bytArray[3] = 4
bytArray[4] = 8
bytArray[5] = 16
bytArray[6] = 32
bytArray[7] = 64
bytArray[8] = 128

'*****Define LCD registers and bits*****
define LCD_BITS      4  
define LCD_LINES     2  ' Set to number of lines for the LCD
Define LCD_DREG      PORTD
Define LCD_DBIT      4  
Define LCD_RSREG     PORTE
Define LCD_RSBIT     0
Define LCD_EREG      PORTE
Define LCD_EBIT      1
define LCD_RWREG     PORTE
define LCD_RWBIT     2
define LCD_COMMANDUS 1500
define LCD_DATAUS    44


'*****Initialize LCD*****
   Low LATE.2  		    ' LCD R/W line low (W)
   Pause 500       	  ' Wait .5 second for LCD to Initialize




mainloop:
    do
        for i = 0 to 8
			workword.byte1 = 0
			workbyte = bytArray[i]		
			gosub NCD8
		next i
        for i = 0 to 8
			workword.byte1 = 0
			workbyte = bytArray[i]		
			gosub NEWNCD8
		next i
        for i = 0 to 8
			mystatus = bytArray[i]		
			gosub checkbit8
		next i
        for i = 0 to 8
			mystatus = bytArray[i]		
			gosub checkbit8ztest
		next i
		for i = 0 to 8        
			mystatus = bytArray[i]
			gosub NCDSUB
        next i
		for i = 0 to 8
			mystatus = bytArray[i]
			gosub LOOKSUB
        next i
		pause 500
            
    loop


NCD8:
' Input: workword (including workbyte)
'Return: bitcount
'Locals: bitcarry
' Notes: If workbyte = 0 then bitcount is set to 0
'       otherwise bitcount = bitnumber (0-7)

    bitcount = 8 ' mov l to w & w to f

    if workbyte = 0 then ' portX was zero
        bitcount = 0
        return
    endif

inloop:
    bitcount = bitcount - 1 ' decf
    workword = workword << 1 ' 2 x rrf with carry
    
    if bitcarry = 0 then 'btfss
        goto inloop ' goto
    endif
	
return

NEWNCD8:
' Input: workword (including workbyte)
'Return: bitcount
'Locals: bitcarry
' Notes: If workbyte = 0 then bitcount is set to 0
'        otherwise bitcount = bitnumber (0-7)

	if workbyte = 0 then 'portX was zero
		bitcount = 0
		return
	endif
	
	bitcount = 8	

	do
		bitcount = bitcount - 1
		workword = workword << 1
	loop while bitcarry = 0

	return
			

checkbit8:
' Input: mystatus
'Return: bitcount
'Locals: none (direct bittest of mystatus
' Notes: If mystatus = 0 then bitcount is not changed
'        otherwise bitcount = bitnumber (0-7) (can be changed to any byte value)
	   
       if mystatus.7 = 1 then
	       bitcount = 7
	       return
       endif
	   if mystatus.6 = 1 then
	       bitcount = 6
	       return
       endif
	   if mystatus.5 = 1 then
	       bitcount = 5
	       return
       endif
	   if mystatus.4 = 1 then
	       bitcount = 4
	       return
       endif
	   if mystatus.3 = 1 then
	       bitcount = 3
	       return
       endif
	   if mystatus.2 = 1 then
	       bitcount = 2
	       return
       endif
	   if mystatus.1 = 1 then
	       bitcount = 1
	       return
       endif
	   if mystatus.0 = 1 then
	       bitcount = 0
	       return
       endif
	
	   return

checkbit8ztest:
' Input: mystatus
'Return: bitcount
'Locals: none (direct bittest of mystatus)
' Notes: If mystatus = 0 then bitcount is not changed (can be changed to any byte value)
'       otherwise bitcount = bitnumber (0-7) (can be changed to any byte value)
	   
       if mystatus = 0 then
			return
       endif			   
       if mystatus.7 = 1 then
	       bitcount = 7
	       return
       endif
	   if mystatus.6 = 1 then
	       bitcount = 6
	       return
       endif
	   if mystatus.5 = 1 then
	       bitcount = 5
	       return
       endif
	   if mystatus.4 = 1 then
	       bitcount = 4
	       return
       endif
	   if mystatus.3 = 1 then
	       bitcount = 3
	       return
       endif
	   if mystatus.2 = 1 then
	       bitcount = 2
	       return
       endif
	   if mystatus.1 = 1 then
	       bitcount = 1
	       return
       endif
	   if mystatus.0 = 1 then
	       bitcount = 0
	       return
       endif
	
	   return


NCDSUB:
' Input: mystatus
'Return: mybyte
'Locals: none (direct bittest of mystatus)
' Notes: If mystatus = 0 then mybyte is not changed
'        otherwise mybyte = bitnumber (1-8) 

    mybyte = NCD mystatus
	
    return
    
LOOKSUB:
' Input: mystatus
'Return: mybyte
'Locals: none (direct bittest of mystatus)
' Notes: If mystatus = 0 then mybyte set to 0
'        otherwise mybyte = bitnumber (1-8) 

    lookdown2 mystatus, <= [%00000000, %00000001, %00000011, %00000111, %00001111, %00011111, %00111111, %01111111, %11111111], mybyte
    
    return

end

Thread: Quickest way to get highest set bit on port in to a variable?

Thread Tools

Search Thread

Display

Threaded View

Re: Quickest way to get highest set bit on port in to a variable?

Similar Threads

highest or lowest variable in an array; how do you find it?

Whats the quickest way to set bits?

Bit set question

set flags within a variable?

How do I to set one bit in a register?

Members who have read this thread : 1

Bookmarks

Bookmarks

Posting Permissions