Infinite loop in hash_value_signed/hash_value_unsigned

[alex@…]

Visual C++ 2012 static analysis found these two infinite loop warnings in hash.hpp:

for(unsigned int i = length * size_t_bits; i > 0; i -= size_t_bits)
{
    seed ^= (std::size_t) (positive >> i) + (seed<<6) + (seed>>2);
}

Warning message:

hash.hpp(156): warning : C6295: Ill-defined for-loop:  'unsigned int' values are always of range '0' to '4294967295'.  Loop executes infinitely.
hash.hpp(176): warning : C6295: Ill-defined for-loop:  'unsigned int' values are always of range '0' to '4294967295'.  Loop executes infinitely.

[Bikineev Anton <abikineev@…>]

pragma warning disable for msvc is added

[Daniel James]

(In [85248]) Fix Visual C++ warning in hash. Refs #8568.

I changed this a little from the patch on #8568. I moved the pragmas to the start and end of the file because I don't like to little the body of the code with them (this does mean I've disabled a potentially useful warning, but the code is pretty stable nowadays).

I also removed the version checks, as the warning should be present in later versions.

[Daniel James]

(In [85389]) Merge Hash. Fixes #8568, Refs #8822.#8822.#8822.

[qiaozhiqiang@…]

unsigned int i, so i >= 0, so i > 0 is i != 0

we should change i > 0 to i != 0 to avoid warning.