boost performance of api converting number to hexadecimal string

bench/lolly/data/numeral_bench.cpp

@@ -0,0 +1,40 @@
+/** \file numeral_bench.cpp
+ *  \copyright GPLv3
+ *  \details Benchmark for converter between numeral and string
+ *  \author jingkaimori
+ *  \date   2024
+ */
+
+#include "lolly/data/numeral.hpp"
+#include <nanobench.h>
+
+using namespace lolly::data;
+
+static ankerl::nanobench::Bench bench;
+
+namespace lolly {
+extern void init_tbox ();
+} // namespace lolly
+
+int
+main () {
+  lolly::init_tbox ();
+#ifdef OS_WASM
+  bench.minEpochIterations (2000);
+#else
+  bench.minEpochIterations (400000);
+#endif
+
+  string hex_string;
+  for (int d= 1; d < 6; d++) {
+    hex_string << ('a' + d % 6);
+    bench.complexityN (d);
+    bench.run ("convert hexadecimal string to int",
+               [&] { from_hex (hex_string); });
+    int hex_number = (0x1 << (d+1)) - 1;
+    bench.run ("convert signed int to hexadecimal string",
+               [&] { to_Hex (hex_number); });
+    bench.run ("convert unsigned int to hexadecimal string",
+               [&] { as_hexadecimal (hex_number, d); });
+  }
+}

lolly/data/numeral.cpp

@@ -154,12 +154,23 @@ to_padded_hex (uint8_t i) {
   return locase_all (to_padded_Hex (i));
 }
 
+template <typename T>
+std::enable_if_t<std::conjunction_v<std::is_integral<T>, std::is_unsigned<T>>,
+                 string>
+to_Hex_positive (T i) {
+  if (i < 16) return hex_string[i & 15];
+  return to_Hex_positive (i >> 4) << hex_string[i & 15];
+}
+
 string
 to_Hex (int32_t i) {
   if (i == INT32_MIN) return "-80000000";
-  if (i < 0) return "-" * to_Hex (-i);
-  if (i < 16) return hex_string[i & 15];
-  return to_Hex (i >> 4) * hex_string[i & 15];
+  if (i < 0) {
+    return string ("-") << to_Hex_positive ((uint32_t) (-i));
+  }
+  else {
+    return to_Hex_positive ((uint32_t) i);
+  };
 }
 
 string
@@ -170,9 +181,12 @@ to_hex (int32_t i) {
 string
 to_Hex (pointer ptr) {
   intptr_t i= (intptr_t) ptr;
-  if (i < 0) return "-" * to_Hex (-i);
-  if (i < 16) return hex_string[i & 15];
-  return to_Hex (i >> 4) * hex_string[i & 15];
+  if (i < 0) {
+    return string ("-") << to_Hex_positive ((uintptr_t) (-i));
+  }
+  else {
+    return to_Hex_positive ((uintptr_t) i);
+  };
 }
 
 string
@@ -196,7 +210,7 @@ from_hex (string s) {
 string
 as_hexadecimal (int i, int len) {
   if (len == 1) return hex_string[i & 15];
-  else return as_hexadecimal (i >> 4, len - 1) * hex_string[i & 15];
+  else return as_hexadecimal (i >> 4, len - 1) << hex_string[i & 15];
 }
 
 } // namespace data

tests/lolly/data/numeral_test.cpp

@@ -155,3 +155,22 @@ TEST_CASE ("to_hex/to_Hex") {
     string_eq (to_hex (INT32_MAX + 1), "-80000000");
   }
 }
+
+TEST_CASE ("as_hexadecimal") {
+  SUBCASE ("0-15 (+/-)") {
+    for (int i= 1; i < 10; i++) {
+      string_eq (as_hexadecimal (i, 1), as_string (i));
+      string_eq (as_hexadecimal (i, 1), as_string (i));
+    }
+    string_eq (as_hexadecimal (0, 1), "0");
+    string_eq (as_hexadecimal (10, 1), "A");
+    string_eq (as_hexadecimal (11, 1), "B");
+    string_eq (as_hexadecimal (12, 1), "C");
+    string_eq (as_hexadecimal (13, 1), "D");
+    string_eq (as_hexadecimal (14, 1), "E");
+    string_eq (as_hexadecimal (15, 1), "F");
+    string_eq (as_hexadecimal (0x12, 2), "12");
+    string_eq (as_hexadecimal (0xABC, 3), "ABC");
+  }
+  SUBCASE ("max") { string_eq (as_hexadecimal (UINT32_MAX, 8), "FFFFFFFF"); }
+}