Optimised *60 and *100
                           ======================
        mdfs.net/Info/Comp/6502/ProgTips/Date/Times60 -- J.G.Harston

When manipulating clock times, you often need to multiply by 60 and 100, for
example centiseconds=((hours*60+minutes)*60+seconds)*100.

This is a small snippet of optimised code to do multiplication by 60 or 100.
There are 360000 = &057E40 centiseconds in a day, so this fits into a 3-byte
24-bit number.

\ Times60 and Times100
\ ====================
\ Fixed multiplication by 60 or 100
\
\ On entry  ws+0..ws+2 = value to multiply
\ On exit   ws+0..ws+2 = resut of multiplication
\           A,X,Y corrupted
\ Size      51 bytes
\ No check for overflow, if the input is greater than 167772 for
\ wsTimes100 or 279620 for wsTimes60 the result will be wrong.
\
 .wsTimes100
 JSR wsTimes10:BCC wsTimes10 :\ n*100
 .wsTimes60
 BIT SETV:JSR wsTimes6or10   :\ n*6
 .wsTimes10
 CLV
 .wsTimes6or10
 JSR wsTimes2                :\ n*2
 LDY ws+2:LDX ws+1:LDA ws+0  :\ n*2
 JSR wsTimes2:BVS wsTimesAdd :\ n*4
 JSR wsTimes2                :\ n*8
 .wsTimesAdd
 ADC ws+0:STA ws+0           :\    n*8+n*2 = n*10
 TXA:ADC ws+1:STA ws+1       :\ or n*4+n*2 = n*6
 TYA:ADC ws+2:STA ws+2
 .SETV
 RTS
 .wsTimes2
 ASL ws+0:ROL ws+1:ROL ws+2:RTS

Along with a routine to add to the current value:
 .wsAdd
  CLC:ADC ws+0:STA ws+0
  LDA #0:ADC ws+1:STA ws+1
  LDA #0:ADC ws+2:STA ws+2
  RTS

a centisecond count can be then calculated with this code:
 LDA #0:STA ws+1:STA ws+2               :\ Clear accumulator
 LDA hours  :STA ws+0:JSR wsTimes60     :\ Hour
 LDA minutes:JSR wsAdd:JSR wsTimes60    :\ Mins
 LDA seconds:JSR wsAdd:JSR wsTimes100   :\ Secs


If you need to preserve X and Y, you can use this alternative code.

\ Times60 and Times100
\ ====================
\ Fixed multiplication by 60 or 100
\
\ On entry  ws+0..ws+2 = value to multiply
\ On exit   ws+0..ws+2 = result of multiplication
\           A corrupted, X,Y preserved
\ Size      56 bytes
\ No check for overflow, if the input is greater than 167772 for
\ wsTimes100 or 279620 for wsTimes60 the result will be wrong.
\
 .wsTimes100
 JSR wsTimes10:JMP wsTimes10            :\ n*100
 .wsTimes60
 BIT SETV:JSR wsTimes6or10              :\ n*6
 .wsTimes10
 CLV
 .wsTimes6or10
 JSR wsTimes2                           :\ n*2
 LDA ws+2:PHA:LDA ws+1:PHA:LDA ws+0:PHA :\ n*2
 JSR wsTimes2:BVS wsTimesAdd            :\ n*4
 JSR wsTimes2                           :\ n*8
 .wsTimesAdd
 PLA:ADC ws+0:STA ws+0                  :\    n*8+n*2 = n*10
 PLA:ADC ws+1:STA ws+1                  :\ or n*4+n*2 = n*6
 PLA:ADC ws+2:STA ws+2
 .SETV
 RTS
 .wsTimes2
 ASL ws+0:ROL ws+1:ROL ws+2:RTS


Credit to gfoot for optimisation using X,Y,A instead of stack:
https://stardot.org.uk/forums/viewtopic.php?p=380521#p380521