Adjustments > Brightness and Contrast: fix potential overflow error

Relates to #452 .  Thank you to @opsimathic for catching and reporting!

Brightness and contrast are possibly the oldest adjustments in PhotoDemon (20+ years old at this point), making this a very old bug!

When calculating average luminance for sampled contrast, I had mistakenly typed integer divide instead of floating-point divide and this can produce an overflow for images whose net brightness exceeds MAX_INT (~4.2e9).

Problem now solved; updated nightly incoming shortly...

Forms/Adjustments_BrightnessContrast.frm

@@ -96,9 +96,9 @@ Attribute VB_Exposed = False
 'Brightness and Contrast Handler
 'Copyright 2001-2022 by Tanner Helland
 'Created: 2/6/01
-'Last updated: 09/June/16
-'Last update: total overhaul; the old code was stupid and slow, and an option is now provided for a modern
-'             L*a*b*-based conversion (via LittleCMS, if available)
+'Last updated: 21/October/22
+'Last update: fix potential overflow due to unintended use of \ instead of /
+'             (see https://github.com/tannerhelland/PhotoDemon/issues/452)
 '
 'Basic brightness/contrast handler.  A legacy LUT-based method is provided, but the modern L*a*b* implementation
 ' (via LittleCMS) is preferred.
@@ -248,9 +248,9 @@ Public Sub BrightnessContrast(ByVal functionParams As String, Optional ByVal toP
                 Else
 
                     Dim rTotal As Single, gTotal As Single, bTotal As Single
-                    rTotal = 0#
-                    gTotal = 0#
-                    bTotal = 0#
+                    rTotal = 0!
+                    gTotal = 0!
+                    bTotal = 0!
 
                     Dim numOfPixels As Long
                     numOfPixels = 0
@@ -265,11 +265,11 @@ Public Sub BrightnessContrast(ByVal functionParams As String, Optional ByVal toP
                     Next x
                     Next y
 
-                    rTotal = rTotal \ numOfPixels
-                    gTotal = gTotal \ numOfPixels
-                    bTotal = bTotal \ numOfPixels
+                    rTotal = rTotal / numOfPixels
+                    gTotal = gTotal / numOfPixels
+                    bTotal = bTotal / numOfPixels
 
-                    imgMean = (rTotal + gTotal + bTotal) \ 3
+                    imgMean = Int((rTotal + gTotal + bTotal) / 3! + 0.5!)
 
                     'As mentioned earlier, cache the sample contrast during preview mode
                     If toPreview Then
@@ -291,7 +291,7 @@ Public Sub BrightnessContrast(ByVal functionParams As String, Optional ByVal toP
                 ctCalc = srcBrightness + (((srcBrightness - imgMean) * newContrast) \ 100)
                 If (ctCalc > 255) Then ctCalc = 255
                 If (ctCalc < 0) Then ctCalc = 0
-                newBCTable(x) = CByte(ctCalc)
+                newBCTable(x) = ctCalc
             Next x
 
         End If

PhotoDemon.vbp

@@ -516,7 +516,7 @@ Description="PhotoDemon Photo Editor"
 CompatibleMode="0"
 MajorVer=9
 MinorVer=0
-RevisionVer=35
+RevisionVer=36
 AutoIncrementVer=1
 ServerSupportFiles=0
 VersionComments="Copyright 2000-2022 Tanner Helland - photodemon.org"