(array) Clean up native code a bit

code/libraries/array/cpp/build.gradle

@@ -18,7 +18,7 @@ apply from: "$rootProject.projectDir/srcsets.gradle"
 // with a shellscript as gradle's c++ tasks are kind of insufferable
 
 tasks.register('compileCpp', Exec) {
-    inputs.files('src/main/cpp/cpphelpers.cpp', 'src/main/public/cpphelpers.h')
+    inputs.files('compile.sh', 'src/main/cpp/cpphelpers.cpp', 'src/main/public/cpphelpers.h')
     outputs.file 'resources/libcpp.so'
     commandLine 'sh', 'compile.sh'
 }

code/libraries/array/cpp/compile.sh

@@ -1,8 +1,10 @@
 #!/usr/bin/env sh
 
-if ! which g++ > /dev/null; then
+CXX=${CXX:-g++}
+
+if ! which ${CXX} > /dev/null; then
     echo "g++ not found, skipping compilation"
     exit 0
 fi
 
-c++ -c -O3 -march=native -shared -fPIC -Isrc/main/public src/main/cpp/*.cpp -o resources/libcpp.so
+${CXX} -O3 -march=native -shared -Isrc/main/public src/main/cpp/*.cpp -o resources/libcpp.so

code/libraries/array/cpp/java/nu/marginalia/NativeAlgos.java

@@ -80,12 +80,14 @@ public class NativeAlgos {
 
             try (var os = new FileOutputStream(tempFile)) {
                 is.transferTo(os);
+                os.flush();
             }
 
             libFile = tempFile.toPath();
             nativeAlgosI = new NativeAlgos(libFile);
         }
         catch (Exception e) {
+            e.printStackTrace();
             logger.info("Failed to load native library, likely not built");
         }
 

code/libraries/array/cpp/src/main/cpp/cpphelpers.cpp

@@ -2,7 +2,17 @@
 #include <algorithm>
 #include <stdio.h>
 
-struct p2 {
+/* Pair of 64-bit integers. */
+/* The struct is packed to ensure that the struct is exactly 16 bytes in size, as we need to pointer
+   alias on an array of 8 byte longs.  Since structs guarantee that the first element is at offset 0,
+   and __attribute__((packed)) guarantees that the struct is exactly 16 bytes in size, the only reasonable
+   implementation is that the struct is laid out as 2 64-bit integers.  This assumption works only as
+   long as there are at most 2 fields.
+
+   This is a non-portable low level hack, but all this code strongly assumes a x86-64 Linux environment.
+   For other environments (e.g. outside of prod), the Java implementation code will have to do.
+*/
+struct __attribute__((packed)) p64x2 {
     int64_t a;
     int64_t b;
 };
@@ -12,29 +22,21 @@ void ms_sort_64(int64_t* area, uint64_t start, uint64_t end) {
 }
 
 void ms_sort_128(int64_t* area, uint64_t start, uint64_t end) {
-  struct p2 *startp = (struct p2 *) &area[start];
-  struct p2 *endp = (struct p2 *) &area[end];
-
-  // sort based on the first element of the pair
-  std::sort(startp, endp, [](struct p2& fst, struct p2& snd) {
+  std::sort(
+    reinterpret_cast<p64x2 *>(&area[start]),
+    reinterpret_cast<p64x2 *>(&area[end]),
+    [](const p64x2& fst, const p64x2& snd) {
     return fst.a < snd.a;
   });
 }
 
-int64_t encodeSearchMiss64(int64_t value) {
+inline int64_t encodeSearchMiss64(int64_t value) {
     return -1 - std::max(int64_t(0), value);
 }
-int64_t encodeSearchMiss128(int64_t value) {
+inline int64_t encodeSearchMiss128(int64_t value) {
     return -2 - std::max(int64_t(0), value);
 }
 
-int64_t decodeSearchMiss64(long value) {
-    return -value - 1;
-}
-int64_t decodeSearchMiss128(long value) {
-    return -value - 2;
-}
-
 int64_t ms_linear_search_64(int64_t key, int64_t* area, uint64_t fromIndex, uint64_t toIndex) {
     uint64_t pos = fromIndex;
     for (; pos < toIndex; pos++) {
@@ -60,30 +62,6 @@ int64_t ms_linear_search_128(int64_t key, int64_t* area, uint64_t fromIndex, uin
     return encodeSearchMiss128(pos - 2);
 }
 
-/**         long low = 0;
-            long high = (toIndex - fromIndex)/sz - 1;
-
-            while (high - low >= LINEAR_SEARCH_CUTOFF) {
-                long mid = (low + high) >>> 1;
-                long midVal = get(fromIndex + sz*mid);
-
-                if (midVal < key)
-                    low = mid + 1;
-                else if (midVal > key)
-                    high = mid - 1;
-                else
-                    return fromIndex + sz*mid;
-            }
-
-            for (fromIndex += low*sz; fromIndex < toIndex; fromIndex+=sz) {
-                long val = get(fromIndex);
-
-                if (val == key) return fromIndex;
-                if (val > key) return encodeSearchMiss(sz, fromIndex);
-            }
-
-            return encodeSearchMiss(sz, toIndex - sz); */
-
 int64_t ms_binary_search_128(int64_t key, int64_t* area, uint64_t fromIndex, uint64_t toIndex) {
    int64_t low = 0;
    int64_t high = (toIndex - fromIndex) / 2 - 1;

code/libraries/array/test/nu/marginalia/array/algo/LongArraySortTest.java

@@ -86,7 +86,7 @@ class LongArraySortTest {
     @Test
     public void quickSortStressTest() throws IOException {
         LongArray array = LongArray.allocate(65536);
-        sortAlgorithmTester(array, LongArraySort::quickSort);
+        sortAlgorithmTester(array, LongArraySort::quickSortJava);
     }
 
     @Test