multiexp: tune which variants to use for which number of points

src/ringct/bulletproofs.cc

@@ -48,7 +48,7 @@ extern "C"
 
 #define PERF_TIMER_START_BP(x) PERF_TIMER_START_UNIT(x, 1000000)
 
-#define STRAUS_SIZE_LIMIT 128
+#define STRAUS_SIZE_LIMIT 232
 #define PIPPENGER_SIZE_LIMIT 0
 
 namespace rct
@@ -77,11 +77,11 @@ static inline rct::key multiexp(const std::vector<MultiexpData> &data, size_t Hi
 {
   if (HiGi_size > 0)
   {
-    static_assert(128 <= STRAUS_SIZE_LIMIT, "Straus in precalc mode can only be calculated till STRAUS_SIZE_LIMIT");
-    return HiGi_size <= 128 && data.size() == HiGi_size ? straus(data, straus_HiGi_cache, 0) : pippenger(data, pippenger_HiGi_cache, HiGi_size, get_pippenger_c(data.size()));
+    static_assert(232 <= STRAUS_SIZE_LIMIT, "Straus in precalc mode can only be calculated till STRAUS_SIZE_LIMIT");
+    return HiGi_size <= 232 && data.size() == HiGi_size ? straus(data, straus_HiGi_cache, 0) : pippenger(data, pippenger_HiGi_cache, HiGi_size, get_pippenger_c(data.size()));
   }
   else
-    return data.size() <= 64 ? straus(data, NULL, 0) : pippenger(data, NULL, 0, get_pippenger_c(data.size()));
+    return data.size() <= 95 ? straus(data, NULL, 0) : pippenger(data, NULL, 0, get_pippenger_c(data.size()));
 }
 
 static inline bool is_reduced(const rct::key &scalar)

src/ringct/multiexp.cc

@@ -79,6 +79,25 @@ extern "C"
 // Best/cached		Straus	Straus	Straus	Straus	Straus	Straus	Straus	Straus	Pip	Pip	Pip	Pip
 // Best/uncached	Straus	Straus	Straus	Straus	Straus	Straus	Pip	Pip	Pip	Pip	Pip	Pip
 
+// New timings:
+//   Pippenger:
+//     2/1 always
+//     3/2 at ~13
+//     4/3 at ~29
+//     5/4 at ~83
+//     6/5 < 200
+//     7/6 at ~470
+//     8/7 at ~1180
+//     9/8 at ~2290
+//   Cached Pippenger:
+//     6/5 < 200
+//     7/6 at 460
+//     8/7 at 1180
+//     9/8 at 2300
+//
+//     Cached Straus/Pippenger cross at 232
+//
+
 namespace rct
 {
 
@@ -543,16 +562,13 @@ skipfirst:
 
 size_t get_pippenger_c(size_t N)
 {
-// uncached: 2:1, 4:2, 8:2, 16:3, 32:4, 64:4, 128:5, 256:6, 512:7, 1024:7, 2048:8, 4096:9
-//   cached: 2:1, 4:2, 8:2, 16:3, 32:4, 64:4, 128:5, 256:6, 512:7, 1024:7, 2048:8, 4096:9
-  if (N <= 2) return 1;
-  if (N <= 8) return 2;
-  if (N <= 16) return 3;
-  if (N <= 64) return 4;
-  if (N <= 128) return 5;
-  if (N <= 256) return 6;
-  if (N <= 1024) return 7;
-  if (N <= 2048) return 8;
+  if (N <= 13) return 2;
+  if (N <= 29) return 3;
+  if (N <= 83) return 4;
+  if (N <= 185) return 5;
+  if (N <= 465) return 6;
+  if (N <= 1180) return 7;
+  if (N <= 2295) return 8;
   return 9;
 }