Use ChaCha20 caching in FastRandomContext

sipa · sipa · commit 5d16f757639e · 2023-01-30T18:12:21.000-05:00
diff --git a/src/random.cpp b/src/random.cpp
@@ -605,12 +605,9 @@ void FastRandomContext::RandomSeed()
 
 uint256 FastRandomContext::rand256() noexcept
 {
-    if (bytebuf_size < 32) {
-        FillByteBuffer();
-    }
+    if (requires_seed) RandomSeed();
     uint256 ret;
-    memcpy(ret.begin(), bytebuf + 64 - bytebuf_size, 32);
-    bytebuf_size -= 32;
+    rng.Keystream(ret.data(), ret.size());
     return ret;
 }
 
@@ -624,7 +621,7 @@ std::vector<unsigned char> FastRandomContext::randbytes(size_t len)
     return ret;
 }
 
-FastRandomContext::FastRandomContext(const uint256& seed) noexcept : requires_seed(false), bytebuf_size(0), bitbuf_size(0)
+FastRandomContext::FastRandomContext(const uint256& seed) noexcept : requires_seed(false), bitbuf_size(0)
 {
     rng.SetKey(seed.begin(), 32);
 }
@@ -675,7 +672,7 @@ bool Random_SanityCheck()
     return true;
 }
 
-FastRandomContext::FastRandomContext(bool fDeterministic) noexcept : requires_seed(!fDeterministic), bytebuf_size(0), bitbuf_size(0)
+FastRandomContext::FastRandomContext(bool fDeterministic) noexcept : requires_seed(!fDeterministic), bitbuf_size(0)
 {
     if (!fDeterministic) {
         return;
@@ -688,12 +685,9 @@ FastRandomContext& FastRandomContext::operator=(FastRandomContext&& from) noexce
 {
     requires_seed = from.requires_seed;
     rng = from.rng;
-    std::copy(std::begin(from.bytebuf), std::end(from.bytebuf), std::begin(bytebuf));
-    bytebuf_size = from.bytebuf_size;
     bitbuf = from.bitbuf;
     bitbuf_size = from.bitbuf_size;
     from.requires_seed = true;
-    from.bytebuf_size = 0;
     from.bitbuf_size = 0;
     return *this;
 }
diff --git a/src/random.h b/src/random.h
@@ -145,23 +145,11 @@ class FastRandomContext
     bool requires_seed;
     ChaCha20 rng;
 
-    unsigned char bytebuf[64];
-    int bytebuf_size;
-
     uint64_t bitbuf;
     int bitbuf_size;
 
     void RandomSeed();
 
-    void FillByteBuffer()
-    {
-        if (requires_seed) {
-            RandomSeed();
-        }
-        rng.Keystream(bytebuf, sizeof(bytebuf));
-        bytebuf_size = sizeof(bytebuf);
-    }
-
     void FillBitBuffer()
     {
         bitbuf = rand64();
@@ -185,10 +173,10 @@ class FastRandomContext
     /** Generate a random 64-bit integer. */
     uint64_t rand64() noexcept
     {
-        if (bytebuf_size < 8) FillByteBuffer();
-        uint64_t ret = ReadLE64(bytebuf + 64 - bytebuf_size);
-        bytebuf_size -= 8;
-        return ret;
+        if (requires_seed) RandomSeed();
+        unsigned char buf[8];
+        rng.Keystream(buf, 8);
+        return ReadLE64(buf);
     }
 
     /** Generate a random (bits)-bit integer. */

Original file line number	Diff line number	Diff line change
`@@ -605,12 +605,9 @@ void FastRandomContext::RandomSeed()`
`605`	`605`
`606`	`606`	`uint256 FastRandomContext::rand256() noexcept`
`607`	`607`	`{`
`608`		`- if (bytebuf_size < 32) {`
`609`		`- FillByteBuffer();`
`610`		`- }`
	`608`	`+ if (requires_seed) RandomSeed();`
`611`	`609`	`uint256 ret;`
`612`		`- memcpy(ret.begin(), bytebuf + 64 - bytebuf_size, 32);`
`613`		`- bytebuf_size -= 32;`
	`610`	`+ rng.Keystream(ret.data(), ret.size());`
`614`	`611`	`return ret;`
`615`	`612`	`}`
`616`	`613`
`@@ -624,7 +621,7 @@ std::vector<unsigned char> FastRandomContext::randbytes(size_t len)`
`624`	`621`	`return ret;`
`625`	`622`	`}`
`626`	`623`
`627`		`-FastRandomContext::FastRandomContext(const uint256& seed) noexcept : requires_seed(false), bytebuf_size(0), bitbuf_size(0)`
	`624`	`+FastRandomContext::FastRandomContext(const uint256& seed) noexcept : requires_seed(false), bitbuf_size(0)`
`628`	`625`	`{`
`629`	`626`	`rng.SetKey(seed.begin(), 32);`
`630`	`627`	`}`
`@@ -675,7 +672,7 @@ bool Random_SanityCheck()`
`675`	`672`	`return true;`
`676`	`673`	`}`
`677`	`674`
`678`		`-FastRandomContext::FastRandomContext(bool fDeterministic) noexcept : requires_seed(!fDeterministic), bytebuf_size(0), bitbuf_size(0)`
	`675`	`+FastRandomContext::FastRandomContext(bool fDeterministic) noexcept : requires_seed(!fDeterministic), bitbuf_size(0)`
`679`	`676`	`{`
`680`	`677`	`if (!fDeterministic) {`
`681`	`678`	`return;`
`@@ -688,12 +685,9 @@ FastRandomContext& FastRandomContext::operator=(FastRandomContext&& from) noexce`
`688`	`685`	`{`
`689`	`686`	`requires_seed = from.requires_seed;`
`690`	`687`	`rng = from.rng;`
`691`		`- std::copy(std::begin(from.bytebuf), std::end(from.bytebuf), std::begin(bytebuf));`
`692`		`- bytebuf_size = from.bytebuf_size;`
`693`	`688`	`bitbuf = from.bitbuf;`
`694`	`689`	`bitbuf_size = from.bitbuf_size;`
`695`	`690`	`from.requires_seed = true;`
`696`		`- from.bytebuf_size = 0;`
`697`	`691`	`from.bitbuf_size = 0;`
`698`	`692`	`return *this;`
`699`	`693`	`}`