The Caml runtime makes a basic distinction between memory pointers and everything else - pointers are mod 2 while everything else is shifted along 1 bit and has the lsb set to 1. This allows for operation of the garbage collector. Integers are in the 'everything else' camp so 0 maps to 1, 1 to 3 ...etc.
The macros Val_int(x) and Int_val(v) allow for conversion to and from caml integer values and appropriate use of these will correct the apparent anomaly.
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Chris Quinn
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