Repaired tuning

libtom · Jun 12, 2024 · a1417cf · a1417cf
1 parent 37ba942
commit a1417cf
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Showing 2 changed files with 26 additions and 11 deletions.
diff --git a/etc/tune.c b/etc/tune.c
@@ -188,11 +188,21 @@ static uint64_t s_time_radix_conversion_read(int size)
    uint64_t t1;
 
    /* "size" is given as "number of limbs" and starts at 8 */
-   length = ((size_t)size - 7u) * MP_DIGIT_BIT;
-
-   /* Over-estimate number of base 10 digits */
-   /* TODO: can overflow with small INT_MAX */
-   length = (length * 28u) / 93u + 2u;
+   length = (size_t)(size * MP_DIGIT_BIT);
+
+   /* Over-estimate number of base 10 digits
+      Magick number: 28/93 = CF(log_10(2))_(p_3, q_3)
+    */
+   written = (length * 28u);
+   /* May happen e.g. if size > 2184  with MP_16BIT
+      but cutoff should be about a couple of thousand bits
+      at most (around or above Karatsuba cutoff).
+    */
+   if (length != written / 28u) {
+      t1 = UINT64_MAX;
+      goto LBL_ERR_1;
+   }
+   length = written / 93u + 2u;
 
    if ((err = random_number(&str_a, length)) != MP_OKAY) {
       t1 = UINT64_MAX;
@@ -659,9 +669,11 @@ int main(int argc, char **argv)
          if (test[n].fn != NULL) {
             s_run(test[n].name, test[n].fn, test[n].cutoff);
             /* TODO: can overflow for small INT_MAX */
-            *test[n].update = ((*test[n].cutoff) * MP_DIGIT_BIT * 93)/28;
+            *test[n].update = (*test[n].cutoff) * MP_DIGIT_BIT;
+            *test[n].cutoff = INT_MAX;
          }
       }
+
    }
    if (args.terse == 1) {
       printf("%d %d %d %d %d %d\n",

diff --git a/s_mp_faster_to_radix.c b/s_mp_faster_to_radix.c
@@ -61,11 +61,14 @@ static mp_err s_mp_to_radix_recursive(const mp_int *a, char **str, size_t *part_
          }
          /* Q = floor(A1 * I / 2^Beta) */
          /* I = floor( (2^(2*Beta)) / B) Here we have R[t] = I, P[t] = B */
-         /* TODO: we don't need the full "a" only  the upper part: a = a_1\beta + a_0 with 0 < a_0 < \beta
-                 (high short-product with s_mp_mul_high).
-                 Problem: s_mp_mul_high does not make use of fast multiplication except COMBA.
-                 (You can do it with Toom-Cook algorithms, but that is work for another day.) */#
-         /*if( (err = s_mp_mul_high(a, &R[t], &q, (a->used/2) + 1) ) != MP_OKAY)                           goto LTM_ERR;*/
+         /* TODO: We don't need the full "a" only  the upper part: a = a_1\beta + a_0 with 0 < a_0 < \beta
+                  The cutoff with s_mp_mul_high is so low that the gap between that and the general cutoff
+                  is too small to be worth the hassle.
+                  But if somebody implements Thom Mulder's short products...
+                  (There are successors. See e.g. D. Harvey and P. Zimmermann "Short Division of Long Integers",
+                   Laszlo Hars "Fast Truncated Multiplication for Cryptographic Applications", Daniel Lemire "Exact Short
+                   Products From Truncated Multipliers", and many^Wsome more.
+          */
          if ((err = mp_mul(a, &R[t], &q)) != MP_OKAY)                                                    goto LTM_ERR;
          if ((err = mp_div_2d(&q, Beta, &q, NULL)) != MP_OKAY)                                           goto LTM_ERR;