_SHL - mkilgore/QB64pe GitHub Wiki

The _SHL function is used to shift the bits of a numerical value to the left.

result = _SHL(numericalVariable, numericalValue)

• numericalVariable is the variable to shift the bits of and can be of the following types: INTEGER, LONG,_INTEGER64, or _BYTE.
• Integer values can be signed or _UNSIGNED.
• numericalValue is the number of places to shift the bits.
• While 0 is a valid value it will have no affect on the variable being shifted.

• Allows for multiplication of a value by 2 faster than normal multiplication (see example 2 below).
• Bits that reach the end of a variable's bit count are dropped (when using a variable of the same type - otherwise they will carry over).
• The type of variable used to store the results should match the type of the variable being shifted.

• Version 1.3 and up.

Example 1:

A~%% = 1 'set right most bit of an_UNSIGNED _BYTE
PRINT A~%%
PRINT _SHL(A~%%,7)
B~%% = _SHL(A~%%,8) 'shift the bit off the left 'edge'
PRINT B~%%

 1
 128
 0

Example 2:

A~%% = 1
FOR I%% = 0 TO 8
    PRINT _SHL(A~%%, I%%)
FOR...NEXT I%%

   1
   2
   4
   8
  16
  32
  64
 128
 256

• Note: When directly PRINTing to screen, the result is calculated internally using a larger variable type so the left most bit is carried to the next value.
  • To avoid this store the result in a variable of the same type before printing.

• _SHR, INTEGER, LONG
• _BYTE, _INTEGER64