Use orthogonal RNG for get_seq()

Twilight-Dream-Of-Magic · Nov 17, 2023 · a34d092 · a34d092
1 parent 4c0672f
commit a34d092
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Showing 3 changed files with 13 additions and 13 deletions.
diff --git a/tests/TextKeysetTest.cpp b/tests/TextKeysetTest.cpp
@@ -239,15 +239,15 @@ static bool WordsKeyImpl( HashFn hash, const seed_t seed, const uint32_t keycoun
                 prefixlen = std::min(len, maxprefix);
                 if (n < lencount[len]) { break; }
                 n      -= lencount[len];
-                rngpos += lencount[len] * (len - prefixlen) + RandSeq::RNGU64_USED;
+                rngpos += lencount[len] * (len - prefixlen) + 1;
             }
             r.seek(rngpos);
             const uint64_t curcount = pow((double)corecount, (double)prefixlen);
             RandSeq rs = r.get_seq(SEQ_NUM, curcount - 1); rs.write(&itemnum, n, 1);
             for (unsigned j = 0; j < prefixlen; j++) {
                 key[j] = coreset[itemnum % corecount]; itemnum /= corecount;
             }
-            r.seek(rngpos + n * (len - prefixlen) + RandSeq::RNGU64_USED);
+            r.seek(rngpos + n * (len - prefixlen) + 1);
             for (unsigned j = prefixlen; j < len; j++) {
                 key[j] = coreset[r.rand_range(corecount)];
             }

diff --git a/util/Random.cpp b/util/Random.cpp
@@ -540,6 +540,8 @@ uint64_t Rand::seq_maxelem( enum RandSeqType seqtype, const uint32_t szelem ) {
 RandSeq Rand::get_seq( enum RandSeqType seqtype, const uint32_t szelem ) {
     RandSeq rs;
 
+    enable_ortho();
+
     // Initialize the Feistel network keys to random 32-bit numbers
     for (uint64_t n = 0; n < RandSeq::FEISTEL_MAXROUNDS; n++) {
         uint64_t r = rand_u64();
@@ -558,10 +560,13 @@ RandSeq Rand::get_seq( enum RandSeqType seqtype, const uint32_t szelem ) {
     rs.rkeys[3] = rand_u64() & ~UINT64_C(1);
     const uint64_t K1 = UINT64_C(0x1BD11BDAA9FC1A22);
     rs.rkeys[4] = K1 ^ rs.rkeys[1] ^ rs.rkeys[2] ^ rs.rkeys[3];
-    // Save the sequence type and element size.
+    // Save the sequence type and element size
     rs.type     = seqtype;
     rs.szelem   = szelem;
 
+    // Consume 1 real random number from the user's POV
+    disable_ortho(1);
+
     return rs;
 }
 
@@ -875,7 +880,7 @@ void RandTest( const unsigned runs ) {
                 RandSeq rs1 = testRands1[k].get_seq(SEQ_NUM, j);
                 rs1.write(&buf64_A[k][0], 0, numgen);
 
-                testRands1[k].seek(testRands1[k].getoffset() - RandSeq::RNGU64_USED);
+                testRands1[k].seek(testRands1[k].getoffset() - 1);
 
                 RandSeq rs2 = testRands1[k].get_seq(SEQ_NUM, j);
                 rs2.write(&buf64_B[k][0], 0, numgen);
@@ -943,7 +948,7 @@ void RandTest( const unsigned runs ) {
                 RandSeq rs1 = testRands1[k].get_seq(SEQ_DIST_1, j);
                 rs1.write(buf8_A, 0, numgen);
 
-                testRands1[k].seek(testRands1[k].getoffset() - RandSeq::RNGU64_USED);
+                testRands1[k].seek(testRands1[k].getoffset() - 1);
 
                 RandSeq rs2 = testRands1[k].get_seq(SEQ_DIST_1, j);
                 rs2.write(buf8_B, 0, numgen);
@@ -1008,7 +1013,7 @@ void RandTest( const unsigned runs ) {
                 RandSeq rs1 = testRands1[k].get_seq(SEQ_DIST_2, j);
                 rs1.write(buf8_A, 0, numgen);
 
-                testRands1[k].seek(testRands1[k].getoffset() - RandSeq::RNGU64_USED);
+                testRands1[k].seek(testRands1[k].getoffset() - 1);
 
                 RandSeq rs2 = testRands1[k].get_seq(SEQ_DIST_2, j);
                 rs2.write(buf8_B, 0, numgen);
@@ -1073,7 +1078,7 @@ void RandTest( const unsigned runs ) {
                 RandSeq rs1 = testRands1[k].get_seq(SEQ_DIST_3, j);
                 rs1.write(buf8_A, 0, numgen);
 
-                testRands1[k].seek(testRands1[k].getoffset() - RandSeq::RNGU64_USED);
+                testRands1[k].seek(testRands1[k].getoffset() - 1);
 
                 RandSeq rs2 = testRands1[k].get_seq(SEQ_DIST_3, j);
                 rs2.write(buf8_B, 0, numgen);

diff --git a/util/Random.h b/util/Random.h
@@ -100,8 +100,7 @@
  *   produce a different sequence of items if its APIs are called multiple
  *   times. If multiple sequences are needed, then multiple RandSeq objects
  *   can be created by repeatedly calling get_seq(). For seeking across
- *   get_seq() calls, each call to get_seq() will use RandSeq::RNGU64_USED
- *   (currently == 7) random numbers.
+ *   get_seq() calls, each call to get_seq() will use 1 random number.
  *
  *   seq_maxelem() will return the maximum possible number of elements in
  *   the sequence type specified. This may be useful to allow a caller to
@@ -382,11 +381,7 @@ class RandSeq {
     // Even though, in theory, only 2 full Feistel rounds are needed for
     // encryption, some smaller block sizes used in Random.cpp require more
     // rounds to get sufficient uniformity of permutations.
-    //
-    // The "- 2" in RNGU64_USED is 1 for the counter and 1 for the
-    // Threefish-defined key, neither of which are random.
     constexpr static unsigned  FEISTEL_MAXROUNDS = 4;
-    constexpr static unsigned  RNGU64_USED       = FEISTEL_MAXROUNDS + Rand::RNG_KEYS - 2;
 
   private:
     friend class Rand;