X-Git-Url: https://git.distorted.org.uk/~mdw/catacomb/blobdiff_plain/bd4902364e73cb062407b972ef7fecef3998d46a..12cc2b760b2bbc3e8fa26c12303e2ea36f3b89da:/math/strongprime.c

diff --git a/math/strongprime.c b/math/strongprime.c
index 5b136534..a12c0d0a 100644
--- a/math/strongprime.c
+++ b/math/strongprime.c
@@ -121,7 +121,10 @@ mp *strongprime_setup(const char *name, mp *d, pfilt *f, unsigned nbits,
 		rabin_iters(nb), pgen_test, &rb)) == 0)
     goto fail_t;
 
-  /* --- Choose a suitable value for %$r = 2it + 1$% for some %$i$% --- */
+  /* --- Choose a suitable value for %$r = 2it + 1$% for some %$i$% --- *
+   *
+   * Then %$r \equiv 1 \pmod{t}$%, i.e., %$r - 1$% is a multiple of %$t$%.
+   */
 
   rr = mp_lsl(rr, t, 1);
   pfilt_create(&c.f, rr);
@@ -137,7 +140,12 @@ mp *strongprime_setup(const char *name, mp *d, pfilt *f, unsigned nbits,
 
   /* --- Select a suitable congruence class for %$p$% --- *
    *
-   * This computes %$p_0 = 2 s (s^{r - 2} \bmod r) - 1$%.
+   * This computes %$p_0 = 2 s (s^{-1} \bmod r) - 1$%.  Then %$p_0 + 1$% is
+   * clearly a multiple of %$s$%, and
+   *
+   *	%$p_0 - 1 \equiv 2 s s^{-1} - 2 \equiv 0 \pmod{r}$%
+   *
+   * is a multiple of %$r$%.
    */
 
   rr = mp_modinv(rr, s, q);