Provide helpers to create integer lists for the given ranges. (#1179)

This can be used together with ArgsProduct() to allow multiple ranges
with different multipliers and mixing dense and sparse ranges.

Example:
BENCHMARK(MyTest)->ArgsProduct({
  CreateRange(0, 1024, /*multi=*/32),
  CreateRange(0, 100, /*multi=*/4),
  CreateDenseRange(0, 4, /*step=*/1)
});

Co-authored-by: Jen-yee Hong <pcmantw@google.com>

README.md

@@ -616,6 +616,23 @@ BENCHMARK(BM_SetInsert)
     ->Args({8<<10, 80});
 ```
 
+For the most common scenarios, helper methods for creating a list of
+integers for a given sparse or dense range are provided.
+
+```c++
+BENCHMARK(BM_SetInsert)
+    ->ArgsProduct({
+      benchmark::CreateRange(8, 128, /*multi=*/2),
+      benchmark::CreateDenseRange(1, 4, /*step=*/1)
+    })
+// would generate the same benchmark arguments as
+BENCHMARK(BM_SetInsert)
+    ->ArgsProduct({
+      {8, 16, 32, 64, 128},
+      {1, 2, 3, 4}
+    });
+```
+
 For more complex patterns of inputs, passing a custom function to `Apply` allows
 programmatic specification of an arbitrary set of arguments on which to run the
 benchmark. The following example enumerates a dense range on one parameter,

include/benchmark/benchmark.h

@@ -1649,6 +1649,21 @@ inline double GetTimeUnitMultiplier(TimeUnit unit) {
   BENCHMARK_UNREACHABLE();
 }
 
+// Creates a list of integer values for the given range and multiplier.
+// This can be used together with ArgsProduct() to allow multiple ranges
+// with different multiplers.
+// Example:
+// ArgsProduct({
+//   CreateRange(0, 1024, /*multi=*/32),
+//   CreateRange(0, 100, /*multi=*/4),
+//   CreateDenseRange(0, 4, /*step=*/1),
+// });
+std::vector<int64_t> CreateRange(int64_t lo, int64_t hi, int multi);
+
+// Creates a list of integer values for the given range and step.
+std::vector<int64_t> CreateDenseRange(int64_t start, int64_t limit,
+                                      int step);
+
 }  // namespace benchmark
 
 #endif  // BENCHMARK_BENCHMARK_H_

src/benchmark_register.cc

@@ -458,4 +458,20 @@ void ClearRegisteredBenchmarks() {
   internal::BenchmarkFamilies::GetInstance()->ClearBenchmarks();
 }
 
+std::vector<int64_t> CreateRange(int64_t lo, int64_t hi, int multi) {
+  std::vector<int64_t> args;
+  internal::AddRange(&args, lo, hi, multi);
+  return args;
+}
+
+std::vector<int64_t> CreateDenseRange(int64_t start, int64_t limit,
+                                      int step) {
+  CHECK_LE(start, limit);
+  std::vector<int64_t> args;
+  for (int64_t arg = start; arg <= limit; arg += step) {
+    args.push_back(arg);
+  }
+  return args;
+}
+
 }  // end namespace benchmark