Noise in Cocoa

gistfile1.m

+ (void)drawNoiseWithOpacity:(CGFloat)opacity inRect:(CGRect)rect{
    static UIImage *noiseImage = nil;     
    static dispatch_once_t oncePredicate;
    dispatch_once(&oncePredicate, ^{
        NSUInteger width = 64, height = 64;
        NSUInteger size = width*height;
        char *rgba = (char *)malloc(size); srand(124);
        for(NSUInteger i=0; i < size; ++i){rgba[i] = rand()%256;}
        CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceGray();
        CGContextRef bitmapContext = 
        CGBitmapContextCreate(rgba, width, height, 8, width, colorSpace, kCGImageAlphaNone);
        CFRelease(colorSpace);
        CGImageRef noiseImageRef = CGBitmapContextCreateImage(bitmapContext);
        CFRelease(bitmapContext);
        free(rgba);
        
        if([[UIScreen mainScreen] respondsToSelector:@selector(scale)] && [[UIScreen mainScreen] scale] == 2){
            noiseImage = [UIImage imageWithCGImage:noiseImageRef scale:2 orientation:UIImageOrientationUp];
        }else{
            noiseImage = [UIImage imageWithCGImage:noiseImageRef];
        }    
        CGImageRelease(noiseImageRef);
    }); 
    
    
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextSaveGState(context);
    CGContextSetAlpha(context, opacity);
    CGContextSetBlendMode(context, kCGBlendModeScreen);
    [noiseImage drawAsPatternInRect:rect];
    CGContextRestoreGState(context);
}