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The hash algorithm has been modified to include a rotate at each step. This should improve the quality of hashes and reduce the number of collisions. However, probably the more important change for performance is to do the modulo computation by repeated subtraction rather than by calling a slow library function.
87 lines
2.4 KiB
NASM
87 lines
2.4 KiB
NASM
mcopy ccommon.macros
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****************************************************************
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*
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* CopyString - copy a string
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*
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* Inputs:
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* toPtr - location to copy to
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* fromPtr - location to copy from
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*
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****************************************************************
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*
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CopyString start cc
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subroutine (4:toPtr,4:fromPtr),0
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short I,M
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lda [fromPtr]
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sta [toPtr]
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tay
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lb1 lda [fromPtr],Y
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sta [toPtr],Y
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dey
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bne lb1
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long I,M
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return
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end
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****************************************************************
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*
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* Hash - find hash displacement
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*
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* Finds the displacement into an array of pointers using a
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* hash function.
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*
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* Inputs:
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* sPtr - points to string to find hash for
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*
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* Outputs:
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* Returns the disp into the hash table
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*
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****************************************************************
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*
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Hash start cc
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hashSize equ 876 # hash buckets - 1
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disp equ 0 disp into hash table
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length equ 2 length of string
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subroutine (4:sPtr),4
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lda [sPtr] set the length of the string
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tax
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and #$00FF
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sta length
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ldy #1 start with char 1
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txa if 1st char is '~', start with char 6
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and #$FF00
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cmp #'~'*256
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bne lb0
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ldy #6
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lb0 lda #0 initial value is 0
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bra lb2 while there are at least 2 chars left
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lb1 asl a rotate sum left one bit
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adc [sPtr],Y add in next two bytes
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iny advance two chars
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iny
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lb2 cpy length
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blt lb1
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bne lb3 if there is 1 char left then
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asl a rotate sum left one bit
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sta disp
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lda [sPtr],Y
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and #$00FF and out the high byte
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adc disp add last byte to the sum
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sec
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lb3 sbc #hashSize+1 disp := (sum mod (hashSize+1)) << 2
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bcs lb3
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adc #hashSize+1
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asl a
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asl a
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sta disp
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return 2:disp return disp
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end
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