From 1686967f1022b6de0352a9027a5df2804cea25b2 Mon Sep 17 00:00:00 2001
From: Richard Thier <magosit@outlook.hu>
Date: Fri, 17 Dec 2021 19:20:58 +0100
Subject: [PATCH] minor tweaks to 4pasu and added 4rot

---
 ypsu.cpp | 75 ++++++++++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 65 insertions(+), 10 deletions(-)

diff --git a/ypsu.cpp b/ypsu.cpp
index 030df79..5d2ffd0 100644
--- a/ypsu.cpp
+++ b/ypsu.cpp
@@ -135,12 +135,9 @@
     free(buf);
   }
 
-  /** Regular memset will not do with thread_local I think... */
-  void my_memset(std::vector<int> &v) {
-    size_t n = v.size();
-    v.clear();
-    v.resize(n);
-    std::fill(v.begin(), v.end(), 0);
+  /** Only werks für das fourpassu! */
+  void my_memset(int *v) {
+    memset(v, 0, (1 << 8) * sizeof(int));
   }
 
   // hand-unrolled fourpass.
@@ -149,10 +146,7 @@
     // alloc helper buffers.
     int sz = n * sizeof(a[0]);
 
-    //std::vector<int> bucketdata(1 << 8);
-    // Below code crashes :-(
-    static std::vector<int> bucketdata(1 << 8);
-    bucketdata.resize(1 << 8); // JHapak's "pattern"
+    static thread_local int bucketdata[1 << 8];
     my_memset(bucketdata);
 
     uint32_t *buf = (uint32_t *)malloc(sz);
@@ -210,6 +204,62 @@
     free(buf);
   }
 
+  static inline uint32_t byterotate(uint32_t x) { return (x >> 8) | (x << 24); }
+  void fourrots(uint32_t *arr, int n) {
+    assert(n * int64_t(sizeof(arr[0])) <= INT_MAX);
+    assert(n % 4 == 0);
+    // alloc helper buffers.
+    int sz = n * sizeof(arr[0]);
+    std::vector<int> bucketdata(1 << 8);
+    int *btd = &bucketdata[0];
+    uint32_t *buf = (uint32_t *)malloc(sz);
+    assert(buf != NULL);
+    uint32_t *src = arr, *dst = buf;
+    uintptr_t swapmask = (uintptr_t)arr ^ (uintptr_t)buf;
+    uint32_t a, b, c, d;
+    uint32_t abt, bbt, cbt, dbt;
+    for (int shift = 0; shift < 32; shift += 8) {
+      memset(btd, 0, bucketdata.size() * sizeof(bucketdata[0]));
+      for (int i = 0; i < n; i += 4) {
+        a = src[i];
+        b = src[i + 1];
+        c = src[i + 2];
+        d = src[i + 3];
+        abt = a & 0xff;
+        bbt = b & 0xff;
+        cbt = c & 0xff;
+        dbt = d & 0xff;
+        btd[abt]++;
+        btd[bbt]++;
+        btd[cbt]++;
+        btd[dbt]++;
+      }
+      int offset = 0;
+      for (int i = 0; i < 1 << 8; i++) {
+        int d = bucketdata[i];
+        bucketdata[i] = offset;
+        offset += d;
+      }
+      for (int i = 0; i < n; i += 4) {
+        a = src[i];
+        b = src[i + 1];
+        c = src[i + 2];
+        d = src[i + 3];
+        abt = a & 0xff;
+        bbt = b & 0xff;
+        cbt = c & 0xff;
+        dbt = d & 0xff;
+        dst[btd[abt]++] = byterotate(a);
+        dst[btd[bbt]++] = byterotate(b);
+        dst[btd[cbt]++] = byterotate(c);
+        dst[btd[dbt]++] = byterotate(d);
+      }
+      src = (uint32_t *)((uintptr_t)src ^ swapmask);
+      dst = (uint32_t *)((uintptr_t)dst ^ swapmask);
+    }
+    free(buf);
+  }
+
   void vsort(uint32_t *a, int n) {
     thread_local std::vector<uint32_t> bts[256];
     #pragma GCC unroll 4
@@ -337,8 +387,13 @@
       measure(inputtype, "4pasu", [&] { fourpassu(&w[0], w.size()); });
       assert(w == expected);
       w = v;
+      measure(inputtype, "4rot", [&] { fourrots(&w[0], w.size()); });
+      assert(w == expected);
+      /*
+      w = v;
       measure(inputtype, "vsort", [&] { vsort(&w[0], w.size()); });
       assert(w == expected);
+      */
 
       for (auto r : results) printf("%9.3fs", r.second);
       puts("");