Re: [Haskell-cafe] Haskell, C and Matrix Multiplication

Ketil Malde wrote:

Blake Rain writes:

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Here is the one in C:

void multiplyM4 (float m1[4][4], float m2[4][4], float m3[4][4]) { m1[0][0] = m2[0][0] * m3[0][0] + m2[0][1] * m3[1][0] + m2[0][2] * m3[2][0] + m2[0][3] * m3[3][0]; m1[0][1] = m2[0][0] * m3[0][1] + m2[0][1] * m3[1][1] + m2[0][2] * m3[2][1] + m2[0][3] * m3[3][1]; (etc) :

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Some points about the C version: : 6. It's pretty fast (being written in C):

Performing 100,000,000 matrix multiples takes on average 6.117s (with gcc -O2). :

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Haskell version:

[foldl (+) 0 $ zipWith (*) x y | x <- m1, y <- transpose m2] : 5. It's very fast (being written in Haskell):

Performing 100,000,000 matrix multiples takes on average 1.435s (with ghc -O2).

This is surprising: a C program doing an explicit list of arithmetic operation is beaten by a factor of 4 or so by a polymorphic, lazy, list-consuming Haskell program? Are you sure? What am I missing?

Constant folding? The numbers certainly depend on the kind of the test program.