Use X64 ASM ed25519 signatures on Linux/x64, which are about 10X faster. Will matter a lot for network controllers, not so much for other things.

ext/ed25519-amd64-asm/sc25519_slide.c

@@ -0,0 +1,49 @@
+#include "sc25519.h"
+
+void sc25519_slide(signed char r[256], const sc25519 *s, int swindowsize)
+{
+  int i,j,k,b,m=(1<<(swindowsize-1))-1, soplen=256;
+  unsigned long long sv0 = s->v[0];
+  unsigned long long sv1 = s->v[1];
+  unsigned long long sv2 = s->v[2];
+  unsigned long long sv3 = s->v[3];
+
+  /* first put the binary expansion into r  */
+  for(i=0;i<64;i++) {
+    r[i] = sv0 & 1;
+    r[i+64] = sv1 & 1;
+    r[i+128] = sv2 & 1;
+    r[i+192] = sv3 & 1;
+    sv0 >>= 1;
+    sv1 >>= 1;
+    sv2 >>= 1;
+    sv3 >>= 1;
+  }
+
+  /* Making it sliding window */
+  for (j = 0;j < soplen;++j) 
+  {
+    if (r[j]) {
+      for (b = 1;b < soplen - j && b <= 6;++b) {
+        if (r[j] + (r[j + b] << b) <= m) 
+        {
+          r[j] += r[j + b] << b; r[j + b] = 0;
+        } 
+        else if (r[j] - (r[j + b] << b) >= -m) 
+        {
+          r[j] -= r[j + b] << b;
+          for (k = j + b;k < soplen;++k) 
+          {
+            if (!r[k]) {
+              r[k] = 1;
+              break;
+            }
+            r[k] = 0;
+          }
+        } 
+        else if (r[j + b])
+          break;
+      }
+    }
+  }
+}