V19 "ENCOD" instruction changes from V18's "TOPONE" instruction
ozpropdev
Posts: 2,791
in Propeller 2
Chip
In V18 we had the "TOPONE" instruction that returns the position of the "top" 1 bit in S into D.
The C flag was set if there were no 1's in D and Z set if result was zero.
It also returns the "top" 1 position of S into D.
A big difference though is C is set to D[0] while Z is set when D is zero.
I personally prefer the V18 version as NC indicated that a valid position value was in D.
Was there a particular reason for this change to C's behaviour?
In V18 we had the "TOPONE" instruction that returns the position of the "top" 1 bit in S into D.
The C flag was set if there were no 1's in D and Z set if result was zero.
$00000000 $00 CZ $00000001 $00 _Z $00000002 $01 __ $00000004 $02 __ $00000008 $03 __ $00000010 $04 __ $00000020 $05 __ $00000040 $06 __ $00000080 $07 __ $00000100 $08 __ $00000200 $09 __ $00000400 $0A __ $00000800 $0B __ $00001000 $0C __ $00002000 $0D __ $00004000 $0E __ $00008000 $0F __ $00010000 $10 __ $00020000 $11 __ $00040000 $12 __ $00080000 $13 __ $00100000 $14 __ $00200000 $15 __ $00400000 $16 __ $00800000 $17 __ $01000000 $18 __ $02000000 $19 __ $04000000 $1A __ $08000000 $1B __ $10000000 $1C __ $20000000 $1D __ $40000000 $1E __ $80000000 $1F _In V19 the instruction was changed to "ENCOD".
It also returns the "top" 1 position of S into D.
A big difference though is C is set to D[0] while Z is set when D is zero.
$00000000 $00 _Z $00000001 $00 _Z $00000002 $01 C_ $00000004 $02 __ $00000008 $03 C_ $00000010 $04 __ $00000020 $05 C_ $00000040 $06 __ $00000080 $07 C_ $00000100 $08 __ $00000200 $09 C_ $00000400 $0A __ $00000800 $0B C_ $00001000 $0C __ $00002000 $0D C_ $00004000 $0E __ $00008000 $0F C_ $00010000 $10 __ $00020000 $11 C_ $00040000 $12 __ $00080000 $13 C_ $00100000 $14 __ $00200000 $15 C_ $00400000 $16 __ $00800000 $17 C_ $01000000 $18 __ $02000000 $19 C_ $04000000 $1A __ $08000000 $1B C_ $10000000 $1C __ $20000000 $1D C_ $40000000 $1E __ $80000000 $1F C_This C flag change slipped under my "P2 Radar" and had me "wheel-spinning" for a while.
I personally prefer the V18 version as NC indicated that a valid position value was in D.
Was there a particular reason for this change to C's behaviour?
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