GMP function

[Kerlingen]

I didn't know GMP before, but I tried to find you code in GMP4 and GMP5. I tried finding the "ror" part, since I think it's very unusual.

The source doesn't contain any matching "ror" in the *.asm files.
The source doesn't contain any matching pseudo-C "ror" like "(x>>n | x<<32-n)" in any file.
The compiled GMP4 and GMP5 libraries don't contain any "ror" instruction.

Maybe it's a different GMP version or different compiler settings where used.

I think the function doesn't modify a "mpf_ptr" structure, the arithmetic operations don't really fit the structure.

[Kerlingen]

_C = D + A - ROR(B, 5)
_A = ROR(C, 15) xor B
_B = C + D
_D = A - ROR(B, 5) + ROR(C, 15) xor B
A = _A
B = _B
C = _C
D = _D

This looks like the inner loop of some hash or crypto function.

A "mpz_struct" doesn't fit either. Both structures contain a pointer and XORing pointers isn't the best idea, even if adding or subtracting is sometimes used with pointers. Do you have a link to the code you're analysing? Just this one code fragment doesn't show much.