From 96b44faa7c9a54be82bda00330b6744abec8aa33 Mon Sep 17 00:00:00 2001
From: Trent Nelson <trent@trent.me>
Date: Fri, 8 Jan 2021 16:30:51 -0800
Subject: [PATCH] Add some glue to handle zeros being returned from the Philox
 4x32 pseudo-RNG.

---
 src/PerfectHash/Rng.h           |  2 +-
 src/PerfectHash/RngPhilox4x32.c | 43 ++++++++++++++++++++++++++++++---
 2 files changed, 41 insertions(+), 4 deletions(-)

diff --git a/src/PerfectHash/Rng.h b/src/PerfectHash/Rng.h
index 33b6d313..bc6c8047 100644
--- a/src/PerfectHash/Rng.h
+++ b/src/PerfectHash/Rng.h
@@ -62,7 +62,7 @@ typedef struct DECLSPEC_ALIGN(16) _RNG_STATE_PHILOX43210 {
     UINT4 Output;
     UINT2 Key;
     ULONG CurrentCount;
-    ULONG Padding;
+    ULONG NumberOfZeroLongsEncountered;
     ULONGLONG TotalCount;
     ULONGLONG TotalBytes;
 } RNG_STATE_PHILOX43210, *PRNG_STATE_PHILOX43210;
diff --git a/src/PerfectHash/RngPhilox4x32.c b/src/PerfectHash/RngPhilox4x32.c
index 88c810da..12e834cc 100644
--- a/src/PerfectHash/RngPhilox4x32.c
+++ b/src/PerfectHash/RngPhilox4x32.c
@@ -330,6 +330,7 @@ RngPhilox43210Init(
     State->Key.X = (ULONG)Rng->Seed;
     State->Key.Y = (ULONG)(Rng->Seed >> 32);
     State->CurrentCount = 0;
+    State->NumberOfZeroLongsEncountered = 0;
     State->TotalCount = 0;
     State->TotalBytes = 0ULL;
     SkipaheadSubsequence(State, Rng->Subsequence);
@@ -352,9 +353,45 @@ RngPhilox43210GenerateRandomBytes(
     Long = (PLONG)Buffer;
 
     for (Index = 0; Index < NumberOfLongs; Index++) {
-        Random = GetRandomLong(State);
-        ASSERT(Random != 0);
-        *Long++ = Random;
+        do {
+            Random = GetRandomLong(State);
+
+            //
+            // I encountered a zero being returned under the following
+            // conditions for State:
+            //
+            //  Counter.X = 0x01c922d1
+            //  Counter.Y = 0x0
+            //  Counter.Z = 0x2
+            //  Counter.W = 0x0
+            //  Key.X = 0x19811025
+            //  Key.Y = 0x20190903
+            //  CurrentCount = 2
+            //  TotalCount = 119835462
+            //  TotalBytes = 479341848
+            //
+            // This was using our default seed, and occurred on the
+            // normaliz-1.keys file in sys32, with the following command line
+            // parameters:
+            //  --FindBestGraph
+            //  --BestCoverageType=LowestNumberOfEmptyCacheLines
+            //  --BestCoverageAttempts=2
+            //  --GraphImpl=1
+            //
+
+            if (Random != 0) {
+                *Long++ = Random;
+                break;
+            }
+
+            State->NumberOfZeroLongsEncountered++;
+
+            //
+            // I picked 10 arbitrarily.
+            //
+
+            ASSERT(State->NumberOfZeroLongsEncountered < 10);
+        } while (1);
     }
 
     return S_OK;