RealBasic loops, arrays and MemoryBlocks
August 24th, 2006
(… following text is my answer to a usenet post ..)
I wrote a test function that makes various speed-checks. The number I
report are in Rosetta emulation, but it does not matter, since they are
“good enough” and the point is not to bench RB against other “native”
languages, but to test RB against itself.
However, running in Windows gaves about a 2x improvement respect to
Rosetta code.
All loops involve 1000000(10e6) iterations (double loop make 1000 * 1000
iterations). I also tried with 10000000 (10e7) iterations and it took
about 10 times more than the 1000000(10e6) iteration. That is to say
bechmarks are linear with number of elements (as expected). I didn’t try
bigger values as it involved paging, thus making quite useless the test.
The first one is a void loop. It takes 0.09 seconds on my MacIntel.
Then I made a double void loop. It takes the same time. That is to say
using two nested for does not take more time.
Then I made a simple loop that copies a variable into another variable.
This runs in 0.17 seconds. Good.
The third loop puts in the variable array elements. 0.17 seconds. The
same. So arrays are well optimized: accessing an element of an array
takes the very same time than accessing a single variable.
I then tried using two dimensional arrays: we get to 0.22 seconds. So
this is slower, but not a *lot* slower (even if for large objects this
+33% can make the difference).
And then memory blocks. I was surprised: 0.3 seconds. It seems that
using memory blocks is slower than using arrays (and in fact there is a
rationale behind this: a lot of people use arrays to store large amounts
of data, they *must* be ultra optimized. I think that MemoryBlocks are
used more often in a different fashion).
#pragma DisableBackgroundTasks
#pragma DisableBoundsChecking
Const LoopSize = 1000000
Const SmallerLoop = 1000
Dim void_start, void_end, arr_start, arr_end As Double
Dim var_start, var_end, mat_start, mat_end As Double
Dim block_start, block_end, dvoid_start, dvoid_end As Double
Dim var As Double
Dim value As Double = 1.0
Dim arr(LoopSize) As Double
Dim mat(SmallerLoop, SmallerLoop) As Double
Dim block As MemoryBlock
for i As Integer = 0 to UBound(arr)
arr(i) = value
next
for i As Integer = 0 to SmallerLoop
for j As Integer = 0 to SmallerLoop
mat(i, j) = 1.0
next
next
block = NewMemoryBlock(LoopSize * 
for i As Integer = 0 To (LoopSize-1) * 8 Step 8
block.DoubleValue(i) = 1.0
next
void_start = Microseconds()
for i As Integer = 0 to LoopSize
next
void_end = Microseconds()
MsgBox "Void loop(" + Str(LoopSize) + "): " + Str((void_end - void_start)/1000000)
dvoid_start = Microseconds()
for i As Integer = 0 to SmallerLoop
for j As Integer = 0 to SmallerLoop
next
next
dvoid_end = Microseconds()
MsgBox "Double void loop(" + Str(LoopSize) + "): " + Str((dvoid_end - dvoid_start)/1000000)
var_start = Microseconds()
for i As Integer = 0 to LoopSize
var = value
next
var_end = Microseconds()
MsgBox "Var loop(" + Str(LoopSize) + "): " + Str((var_end - var_start)/1000000)
arr_start = Microseconds()
for i As Integer = 0 to LoopSize
var = value
next
arr_end = Microseconds()
MsgBox "Arr loop(" + Str(LoopSize) + "): " + Str((arr_end - arr_start)/1000000)
mat_start = Microseconds()
for i As Integer = 0 to SmallerLoop
for j As Integer = 0 to SmallerLoop
var = mat(i, j)
next
next
mat_end = Microseconds()
MsgBox "Mat loop(" + Str(LoopSize) + "): " + Str((mat_end - mat_start)/1000000)
block_start = Microseconds()
for i As Integer = 0 To (LoopSize-1) * 8 Step 8
var = block.DoubleValue(i)
next
block_end = Microseconds()
MsgBox "Block loop(" + Str(LoopSize) + "): " + Str((block_end - block_start)/1000000)
block_start = Microseconds()
for i As Integer = 0 To (LoopSize-1)
var = block.DoubleValue(i*8)
next
block_end = Microseconds()
MsgBox "Block loop(" + Str(LoopSize) + "): " + Str((block_end - block_start)/1000000)
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