From f6edd3286d4bb8ed6484ad2cd7d87a55ccc41f3b Mon Sep 17 00:00:00 2001
From: Marco Bodrato <bodrato@mail.dm.unipi.it>
Date: Sat, 28 Nov 2020 23:36:54 +0100
Subject: primesieve.c: Differentiate n_to_bit into floor and ceil.

---
 primesieve.c | 46 +++++++++++++++++++++++++---------------------
 1 file changed, 25 insertions(+), 21 deletions(-)

(limited to 'primesieve.c')

diff --git a/primesieve.c b/primesieve.c
index 279e8d367..6922025c8 100644
--- a/primesieve.c
+++ b/primesieve.c
@@ -46,13 +46,17 @@ bit_to_n (mp_limb_t bit) { return (bit*3+4)|1; }
 static mp_limb_t
 id_to_n  (mp_limb_t id)  { return id*3+1+(id&1); }
 
-/* n_to_bit (n) = ((n-1)&(-CNST_LIMB(2)))/3U-1 */
+/* n_fto_bit (n) = ((n-1)&(-CNST_LIMB(2)))/3U-1 */
 static mp_limb_t
-n_to_bit (mp_limb_t n) { return ((n-5)|1)/3U; }
+n_fto_bit (mp_limb_t n) { return ((n-5)|1)/3U; }
+
+/* n_cto_bit (n) = ((n-2)&(-CNST_LIMB(2)))/3U */
+static mp_limb_t
+n_cto_bit (mp_limb_t n) { return (n|1)/3U-1; }
 
 #if 0
 static mp_size_t
-primesieve_size (mp_limb_t n) { return n_to_bit(n) / GMP_LIMB_BITS + 1; }
+primesieve_size (mp_limb_t n) { return n_fto_bit(n) / GMP_LIMB_BITS + 1; }
 #endif
 
 #if GMP_LIMB_BITS > 61
@@ -65,7 +69,7 @@ primesieve_size (mp_limb_t n) { return n_to_bit(n) / GMP_LIMB_BITS + 1; }
 #define SIEVE_2MSK1 CNST_LIMB(0x9402180c40230184)
 #define SIEVE_2MSK2 CNST_LIMB(0x0285021088402120)
 #define SIEVE_2MSKT CNST_LIMB(0xa41210084421)
-#define SEED_LIMIT 288
+#define SEED_LIMIT (17*17-1)
 #else
 #define SEED_LIMIT 202
 #endif
@@ -77,7 +81,7 @@ primesieve_size (mp_limb_t n) { return n_to_bit(n) / GMP_LIMB_BITS + 1; }
 #define SIEVE_MASK1 CNST_LIMB(0x12148960)
 #define SIEVE_MASK2 CNST_LIMB(0x44a120cc)
 #define SIEVE_MASKT CNST_LIMB(0x1a)
-#define SEED_LIMIT 120
+#define SEED_LIMIT (11*11-1)
 #else
 #define SEED_LIMIT 114
 #endif
@@ -91,7 +95,7 @@ primesieve_size (mp_limb_t n) { return n_to_bit(n) / GMP_LIMB_BITS + 1; }
 #define SEED_LIMIT 34
 #else
 #define SIEVE_SEED CNST_LIMB(0x0)
-#define SEED_LIMIT 24
+#define SEED_LIMIT (5*5-1)
 #endif /* 7 */
 #endif /* 15 */
 #endif /* 30 */
@@ -193,10 +197,10 @@ fill_bitpattern (mp_ptr bit_array, mp_size_t limbs, mp_limb_t offset)
     m22 = SIEVE_2MSK2;
     m23 = SIEVE_2MSKT;
   } else { /* correctly handle offset == 0... */
-    m21 = offset % 110;
-    SET_OFF1 (m11, m12, SIEVE_MASK1, SIEVE_MASKT, m21, 110);
-    offset %= 182;
-    SET_OFF2 (m21, m22, m23, SIEVE_2MSK1, SIEVE_2MSK2, SIEVE_2MSKT, offset, 182);
+    m21 = offset % (11 * 5 * 2);
+    SET_OFF1 (m11, m12, SIEVE_MASK1, SIEVE_MASKT, m21, 11 * 5 * 2);
+    offset %= 13 * 7 * 2;
+    SET_OFF2 (m21, m22, m23, SIEVE_2MSK1, SIEVE_2MSK2, SIEVE_2MSKT, offset, 13 * 7 * 2);
   }
   /* THINK: Consider handling odd values of 'limbs' outside the loop,
      to have a single exit condition. */
@@ -204,13 +208,13 @@ fill_bitpattern (mp_ptr bit_array, mp_size_t limbs, mp_limb_t offset)
     bit_array[0] = m11 | m21;
     if (--limbs == 0)
       break;
-    ROTATE1 (m11, m12, 110);
+    ROTATE1 (m11, m12, 11 * 5 * 2);
     bit_array[1] = m11 | m22;
     bit_array += 2;
-    ROTATE1 (m11, m12, 110);
-    ROTATE2 (m21, m22, m23, 182);
+    ROTATE1 (m11, m12, 11 * 5 * 2);
+    ROTATE2 (m21, m22, m23, 13 * 7 * 2);
   } while (--limbs != 0);
-  return 4;
+  return n_cto_bit (13 + 1);
 #else
 #ifdef SIEVE_MASK2
   mp_limb_t mask, mask2, tail;
@@ -220,8 +224,8 @@ fill_bitpattern (mp_ptr bit_array, mp_size_t limbs, mp_limb_t offset)
     mask2 = SIEVE_MASK2;
     tail = SIEVE_MASKT;
   } else { /* correctly handle offset == 0... */
-    offset %= 70;
-    SET_OFF2 (mask, mask2, tail, SIEVE_MASK1, SIEVE_MASK2, SIEVE_MASKT, offset, 70);
+    offset %= 7 * 5 * 2;
+    SET_OFF2 (mask, mask2, tail, SIEVE_MASK1, SIEVE_MASK2, SIEVE_MASKT, offset, 7 * 5 * 2);
   }
   /* THINK: Consider handling odd values of 'limbs' outside the loop,
      to have a single exit condition. */
@@ -231,9 +235,9 @@ fill_bitpattern (mp_ptr bit_array, mp_size_t limbs, mp_limb_t offset)
       break;
     bit_array[1] = mask2;
     bit_array += 2;
-    ROTATE2 (mask, mask2, tail, 70);
+    ROTATE2 (mask, mask2, tail, 7 * 5 * 2);
   } while (--limbs != 0);
-  return 2;
+  return n_cto_bit (7 + 1);
 #else
   MPN_FILL (bit_array, limbs, CNST_LIMB(0));
   return 0;
@@ -249,7 +253,7 @@ first_block_primesieve (mp_ptr bit_array, mp_limb_t n)
 
   ASSERT (n > 4);
 
-  bits  = n_to_bit(n);
+  bits  = n_fto_bit(n);
   limbs = bits / GMP_LIMB_BITS;
 
   if (limbs != 0)
@@ -264,7 +268,7 @@ first_block_primesieve (mp_ptr bit_array, mp_limb_t n)
 
     ASSERT (i < GMP_LIMB_BITS);
 
-    if (n_to_bit (SEED_LIMIT + 1) < GMP_LIMB_BITS)
+    if (n_cto_bit (SEED_LIMIT) < GMP_LIMB_BITS)
       i = 0;
     mask = CNST_LIMB(1) << i;
     index = 0;
@@ -400,7 +404,7 @@ gmp_primesieve (mp_ptr bit_array, mp_limb_t n)
 
   ASSERT (n > 4);
 
-  bits = n_to_bit(n);
+  bits = n_fto_bit(n);
   size = bits / GMP_LIMB_BITS + 1;
 
   if (size > BLOCK_SIZE * 2) {
-- 
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