nn_modinv_fermat_redc
ATTRIBUTE_WARN_UNUSED_RET int nn_modinv_fermat_redc(nn_t out, nn_src_t x, nn_src_t p, nn_src_t r, nn_src_t r_square, word_t mpinv);
ret = nn_modinv_fermat_redc(&(out->fp_val), &(in->fp_val), &(in->ctx->p), &(in->ctx->r), &(in->ctx->r_square), in->ctx->mpinv);