bigarrays much lower than normal ones
 Hal Daume III
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Date:  20041031 (16:06) 
From:  Hal Daume III <hdaume@I...> 
Subject:  bigarrays much lower than normal ones 
I've been hitting the limiting size of normal float arrays and was having a look at the Bigarray module. Unfortunately, it seems roughly 34 times *slower* than the standard array, which is pretty much unacceptable for me. Am I doing something naively wrong, or are the Bigarrays truly this slow? The timing results I get (i686, redhat) are along the liens of: stdarray, safe: 12.000u 0.030s 0:12.18 98.7% 0+0k 0+0io 107pf+0w 12.060u 0.030s 0:12.22 98.9% 0+0k 0+0io 107pf+0w stdarray, unsafe: 11.990u 0.070s 0:12.21 98.7% 0+0k 0+0io 107pf+0w 12.130u 0.040s 0:12.31 98.8% 0+0k 0+0io 107pf+0w bigarray, 64 bit: 39.760u 0.040s 0:40.35 98.6% 0+0k 0+0io 110pf+0w 39.750u 0.030s 0:40.09 99.2% 0+0k 0+0io 110pf+0w bigarray, 32 bit: 41.950u 0.050s 0:42.60 98.5% 0+0k 0+0io 110pf+0w 42.070u 0.040s 0:42.53 99.0% 0+0k 0+0io 110pf+0w (safe vs. unsafe is when compiled normally or with unsafe; 64bit vs 32bit is the 'kind' used for the bigarrays.) I'm also really shocked that the 32 bit float bigarrays are slower than the 64 bit ones! Can someone explain this to me? The code is: <standard array> open Array let normalize a = let s = fold_left (+.) 0. a in for i = 0 to length a  1 do a.(i) < a.(i) /. s; done; () let _ = let a = make 1000000 0. in for iter = 1 to 100 do for i = 0 to 999999 do let i' = float_of_int i in a.(i) < log (0.01 *. i' *. i' +. 3. *. i' +. 4.); done; normalize a; done; () <big array> open Bigarray let normalize a = let _N = Array1.dim a in let rec sum n acc = if n >= _N then acc else sum (n+1) (acc +. Array1.get a n) in let s = sum 0 0. in for i = 0 to _N  1 do Array1.set a i (Array1.get a i /. s); done; () let _ = let a = Array1.create float32 c_layout 1000000 in for iter = 1 to 100 do for i = 0 to 999999 do let i' = float_of_int i in Array1.set a i (log (0.01 *. i' *. i' +. 3. *. i' +. 4.)); done; normalize a; done; () If you put the array allocation inside the iter loop, nothing changes much, relatively, on the timing results.  Hal  Hal Daume III  hdaume@isi.edu "Arrest this man, he talks in maths."  www.isi.edu/~hdaume