[Prelim patch] Speed up ints parsing

[Paolo Carlini]

Hi,

you find attached to this message what I have ready, in case
someone wants to play with it: I plan to refine it and post
a final version during the weekend or at most on monday.

The testsuite is ok, some more tests are ok, and the performance
are pretty good. Reading back a file containing 3000000 ints
(from 0 to 2999999) via:

  int j;
  for (int i = 0; i < 3000000; i++)
    std::cin >> j;

takes, on my P4-2400 (-O2):

3.4
---
18.740u 0.030s 0:19.59 95.8%    0+0k 0+0io 208pf+0w

3.4 + this patch
----------------
9.940u 0.030s 0:10.40 95.8%     0+0k 0+0io 197pf+0w


So, almost a 2x speed gain (besides the major code clean up!)


Ciao for now,
Paolo.

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