On Apr 3, 2009, at 11:31 AM, leppie wrote:
I will ask on the R6RS mailing about the rationale for this.
Since as usual, we're not going to achieve anything positive
on r6rs-discuss, here is my suggestion to Eduardo and anybody
else who wants to use the hash functions.
The typical use of string-hash is to obtain an integer value
from which an index into a vector is computed. There are two
cases for the vector length N:
1. N is a power of 2. In this case, you compute the index
into the vector using
(bitwise-logand (string-hash ---) (- N 1))
This returns a valid index between 0 and (- N 1) inclusive.
2. N is not known to be a power of 2. In this case, you
compute the index using
(mod (string-hash ---) N)
This case too returns a valid index between 0 and (- N 1)
inclusive.
In either case, it does not matter if the value returned by
string-hash is positive, negative, or 0; you get the correct
answer anyways. So, there is no need or utility for limiting
the value returned by string-hash to nonnegative integers.
Aziz,,,
