Speed optimization in REALbasic Code.

Today someone asked why this code is very slow:

// Methods
  Sub Slow()
    // Takes over 15 minutes here
    
    dim t as integer = ticks
    
    dim mem as MemoryBlock = NewMemoryBlock(128*1024*1024)
    dim n as integer
    
    for n=0 to len(mem)
      mem.Byte(n)=rnd*255
    next n
    
    t = ticks-t
    MsgBox str(t/60)+" seconds"
End Sub>

now calling len(mem) here does the following:

Create a copy of the memoryblock as a string.
Lookup the length of this string.
Destroy the string.

And this happens all 128 million times! This takes forever. The solution is easy: Use mem.size instead of len(mem) you can save a magnitude of time. Also you should keep the upper bound of the for loop in a local variable for even faster code:

Sub Better()
    // Takes 27 seconds here
    
    dim t as integer = ticks
    
    dim mem as MemoryBlock = NewMemoryBlock(128*1024*1024)
    dim n as integer
    
    dim c as integer = mem.size-1
    for n=0 to c
      mem.Byte(n)=rnd*255
    next n
    
    t = ticks-t
    MsgBox str(t/60)+" seconds"
End Sub

You can even optimize it more by using the Random class and requesting a random value in a given range. Integer math is faster here than double math:

Sub Best()
    // Takes 21 seconds here
    
    dim t as integer = ticks
    
    dim mem as MemoryBlock = NewMemoryBlock(128*1024*1024)
    dim n as integer
    dim r as new Random
    
    dim c as integer = mem.size-1
    for n=0 to c
      mem.Byte(n)=r.InRange(0,255)
    next n
    
    t = ticks-t
    MsgBox str(t/60)+" seconds"
End Sub

PS: Code formatted with my format script: monkeybreadsoftware.de/realbasic/format.shtml Claris FileMaker Plugin