Add accumulated index calculator with tests.

 * This will replace batch_ids/item_ids arrays for offloading,
   greatly saving the memory footprint.

 * Adds a standardized return (error) codes for NBA internal APIs.

include/nba/core/accumidx.hh

@@ -0,0 +1,39 @@
+#ifndef __NBA_CORE_ACCUMIDX_HH__
+#define __NBA_CORE_ACCUMIDX_HH__
+
+#include <nba/core/errors.hh>
+#include <type_traits>
+
+namespace nba {
+
+template<typename T>
+static inline nba::error_t get_accum_idx(const T *group_counts,
+                                         const T num_groups,
+                                         const T global_idx,
+                                         T &group_idx,
+                                         T &item_idx)
+{
+    static_assert(std::is_integral<T>::value, "Integer type required.");
+    T sum = 0;
+    T i;
+    bool found = false;
+    for (i = 0; i < num_groups; i++) {
+        if (global_idx >= sum && global_idx < sum + group_counts[i]) {
+            item_idx = global_idx - sum;
+            found = true;
+            break;
+        }
+        sum += group_counts[i];
+    }
+    if (found)
+        group_idx = i;
+    else
+        return NBA_NOT_FOUND;
+    return NBA_SUCCESS;
+}
+
+} // endns(nba)
+
+#endif
+
+// vim: ts=8 sts=4 sw=4 et

include/nba/core/errors.hh

@@ -0,0 +1,16 @@
+#ifndef __NBA_CORE_ERRORS_HH__
+#define __NBA_CORE_ERRORS_HH__
+
+namespace nba {
+
+typedef enum : int {
+    NBA_SUCCESS = 0,
+    NBA_FAILURE = 1,
+    NBA_NOT_FOUND = 2,
+} error_t;
+
+} // endns(nba)
+
+#endif
+
+// vim: ts=8 sts=4 sw=4 et

tests/test_accumidx.cc

@@ -0,0 +1,43 @@
+#include <nba/core/errors.hh>
+#include <nba/core/accumidx.hh>
+#include <gtest/gtest.h>
+
+using namespace std;
+using namespace nba;
+
+TEST(AccumIdxTest, Count) {
+    const unsigned num_groups = 4;
+    const unsigned groups[num_groups] = { 35, 1, 0, 21 };
+    unsigned group_idx = 0, item_idx = 0;
+    EXPECT_EQ(NBA_SUCCESS, get_accum_idx(groups, num_groups, 0u, group_idx, item_idx));
+    EXPECT_EQ(0, group_idx);
+    EXPECT_EQ(0, item_idx);
+    EXPECT_EQ(NBA_SUCCESS, get_accum_idx(groups, num_groups, 1u, group_idx, item_idx));
+    EXPECT_EQ(0, group_idx);
+    EXPECT_EQ(1, item_idx);
+    EXPECT_EQ(NBA_SUCCESS, get_accum_idx(groups, num_groups, 17u, group_idx, item_idx));
+    EXPECT_EQ(0, group_idx);
+    EXPECT_EQ(17, item_idx);
+    EXPECT_EQ(NBA_SUCCESS, get_accum_idx(groups, num_groups, 34u, group_idx, item_idx));
+    EXPECT_EQ(0, group_idx);
+    EXPECT_EQ(34, item_idx);
+    EXPECT_EQ(NBA_SUCCESS, get_accum_idx(groups, num_groups, 35u, group_idx, item_idx));
+    EXPECT_EQ(1, group_idx);
+    EXPECT_EQ(0, item_idx);
+    EXPECT_EQ(NBA_SUCCESS, get_accum_idx(groups, num_groups, 36u, group_idx, item_idx));
+    EXPECT_EQ(3, group_idx);
+    EXPECT_EQ(0, item_idx);
+    EXPECT_EQ(NBA_SUCCESS, get_accum_idx(groups, num_groups, 37u, group_idx, item_idx));
+    EXPECT_EQ(3, group_idx);
+    EXPECT_EQ(1, item_idx);
+    EXPECT_EQ(NBA_SUCCESS, get_accum_idx(groups, num_groups, 56u, group_idx, item_idx));
+    EXPECT_EQ(3, group_idx);
+    EXPECT_EQ(20, item_idx);
+    group_idx = 7;
+    item_idx = 7;
+    EXPECT_EQ(NBA_NOT_FOUND, get_accum_idx(groups, num_groups, 57u, group_idx, item_idx));
+    EXPECT_EQ(7, group_idx);
+    EXPECT_EQ(7, item_idx);
+}
+
+// vim: ts=8 sts=4 sw=4 et