Set individual bits in a bank

This code has been declared by its author to be Public Domain code.

Set individual bits in a bank by Andy

2009

B3D only allows you to read or write to a bank in multiples of 8 bits.

*Byte(8 bits)
*Short(16 bits)
*Int(32 bits)

These functions simply enable you to write and read individual bits in a bank(up to 255MB in size). It also enables you to read the last bit position in the bank. It can be useful for bit flags or compression.

Functions:
bit_read(bank, offset%)
*Returns the bit at offset% of bank
*offset% should be of type Int

bit_write(bank, offset%, bit)
*Writes the bit at offset% of bank with a bit value of either 0 or 1
*offset% should be of type Int

bit_last(bank)
*Returns the last bit in bank, effectively the size in bits-1.

Usage:
bank - the name of the bank you wish to manipulate.
offset% - the position of the bit you wish to set.
bit - the binary value you want the bit to have(0 or 1).

Remember that offset% begins at 0.

; Create the bank to use
bnktest=CreateBank(120) 

; set the first 16 bits of the bank to alternating 1/0 
For q%=0 To 15 Step 2
bit_write(bnktest, q%, 1)
Next 

; Read and display the first 16 bits of the bank
For q%= 0 To 15
a=bit_read(bnktest,q%)
Print a
Next
Print
; Read and display the last bit position in the bank
Print "The last bit position in bank is "+bit_last(bnktest)

WaitKey()


Function bit_read(bank, offset%)
b=offset% Mod 8
c%=(offset%-b)/8
a=PeekByte(bank,c%)
Return (a Shr (b )) And 1
End Function

Function bit_write(bank, offset%, bit)
b=offset% Mod 8
c%=(offset%-b)/8
a=PeekByte(bank,c%)
If bit <>0 Then
   a=a Or (bit Shl (b))
Else
   a=a And (bit Shl (b))
EndIf
PokeByte bank,c%,a
End Function

Function bit_last(bank)
a%=BankSize(bank)*8
Return a%-1
End Function

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