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On Thu, 22 Jan 2009, David Manura wrote:

Date: Thu, 22 Jan 2009 07:37:20 -0500 (EST)
From: Leo Razoumov
In Lua, on the other hand, some
optimizations make code *MORE* readable.

Here's one optimization that is less readable:

 local y = myvar^4 / (1 + myvar^2)

 local x2 = myvar*myvar
 local y = x2*x2 / (1 + x2)
 -- Lua itself couldn't do this factorization due to
 -- the possibility not only of overflow but also
 -- metamethods, except in special cases if detected
 -- by code analysis

The optimization above is, in essence, an *algorithmic* optimization
rather than a programming optimization. You are defining your own way of raising number to some power relying upon associativity of multiplication. In a finite precision math, such optimization could lead to non-bit-exact results when compared with an unoptimized case. I really do not want my compiler to do such things for me behind the scenes.

By the same token the following function

function mysum1(x)
	local sum=1
	for i=1,9999 do
		sum= sum + x^i
	return sum

can be "optimized" into

function mysum2(x)
	return 1/(1-x)

x= 0.5
print(mysum1(x), mysum2(x), mysum1(x) - mysum2(x))
assert(mysum1(x) == mysum2(x))