Using arrays in asm

kenmac

Hi folks,
What is the best method of storing/reading data in array elements in asm coding?

kenmac

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Perth, Western Australia
Time Zone = GMT + 8

Baggers

Hi kenmac, it depends on your array size.

if it's a nice power of two size, say 8x8 bytes for example

'getentry Yoffset, Xoffset   gets    arrayptr[noparse][[/noparse]y][noparse][[/noparse]x] for an ANYx32 array
getentry
  mov ptr,Yoffset
  shl ptr,#5 ' shl ptr,#5 is same as ptr:=ptr*32
  add ptr,Xoffset
  add ptr,arrayptr
  rdbyte value,ptr
getentry_ret
  ret
ptr long 0
arrayptr long somewhereinhubram
value long 0

or if it's an easily obtainable size, ie not too many bits to make the value to multiply the Y by, eg 40

'getentry Yoffset, Xoffset   gets    arrayptr[noparse][[/noparse]y][noparse][[/noparse]x] for an ANYx40 array
getentry
  mov ptr,Yoffset
  shl ptr,#2           ' = Yoffset*4
  add ptr,Yoffset    ' = Yoffset*5
  shl ptr,#3           ' = Yoffset*5*8 = *40
  add ptr,Xoffset
  add ptr,arrayptr
  rdbyte value,ptr
getentry_ret
  ret
ptr long 0
arrayptr long somewhereinhubram
value long 0

if it's a nice power of two size, say 8x8 words for example

'getentry Yoffset, Xoffset   gets    arrayptr[noparse][[/noparse]y][noparse][[/noparse]x] for an ANYx32 array
getentry
  mov ptr,Yoffset
  shl ptr,#5 ' shl ptr,#5 is same as ptr:=ptr*32
  add ptr,Xoffset
  shl ptr,#1 ' shl ptr,#1 multiplies ptr by two for words
  add ptr,arrayptr
  rdword value,ptr
getentry_ret
  ret
ptr long 0
arrayptr long somewhereinhubram
value long 0

or if it's an easily obtainable size, ie not too many bits to make the value to multiply the Y by, eg 40

'getentry Yoffset, Xoffset   gets    arrayptr[noparse][[/noparse]y][noparse][[/noparse]x] for an ANYx40 array
getentry
  mov ptr,Yoffset
  shl ptr,#2           ' = Yoffset*4
  add ptr,Yoffset    ' = Yoffset*5
  shl ptr,#3           ' = Yoffset*5*8 = *40
  add ptr,Xoffset
  shl ptr,#1 ' shl ptr,#1 multiplies ptr by two for words
  add ptr,arrayptr
  rdword value,ptr
getentry_ret
  ret
ptr long 0
arrayptr long somewhereinhubram
value long 0

otherwise you'll have to use a multiply

'getentry Yoffset, Xoffset   gets    arrayptr[noparse][[/noparse]y][noparse][[/noparse]x] for an ANYxANY array ( ANYx175 in this example )
getentry
  mov multiplyA,Yoffset
  mov multiplyB,arraywidth
  call #multiplyAandB
  mov ptr,multiplyAnswer
  add ptr,Xoffset
  add ptr,arrayptr
  rdword value,ptr
getentry_ret
  ret
ptr long 0
arrayptr long somewhereinhubram
arraywidth long 175
value long 0

also, I've not put any boundary check in there, to keep the entries from getting data outside the array etc. but I'm sure you could add that yourself.

and for storing change rdbyte to wrbyte, etc. obviously copied into another routine so you don't change reading to storing [noparse]:D[/noparse]

hope this helps.

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