--- nono/lib/mystring.cpp	2026/04/29 17:04:57	1.1.1.5
+++ nono/lib/mystring.cpp	2026/04/29 17:05:08	1.1.1.6
@@ -4,6 +4,10 @@
 // Licensed under nono-license.txt
 //
 
+//
+// 文字列操作
+//
+
 #include "mystring.h"
 #include <algorithm>
 
@@ -141,25 +145,59 @@ string_split(const char *str, int len, c
 	return list;
 }
 
-#if 0
+// val を3桁ずつカンマ区切りした文字列にして返す。最大は 26桁。
+// ex) 123   -> "138"
+//     12345 -> "12,345"
+std::string
+format_number(uint64 val)
+{
+	//                 1   2   3   4   5   6
+	// UINT64_MAX = 18,446,744,073,709,551,615
+	char part[6][8];
+	char buf[32];
+	int n;
+
+	n = 0;
+	memset(&part, 0, sizeof(part));
+	while (val >= 1000) {
+		uint32 r = val % 1000;
+		val /= 1000;
+
+		snprintf(part[n], sizeof(part[n]), ",%03u", r);
+		n++;
+	}
+	// この時点で
+	// part[0] = ",615";
+	// part[1] = ",551";
+	// :
+	// part[5] = ",446";
+
+	// 先頭(val は 1000未満)
+	snprintf(buf, sizeof(buf), "%u", (uint32)val);
+
+	// part を連結
+	while (--n >= 0) {
+		strlcat(buf, part[n], sizeof(buf));
+	}
+	return std::string(buf);
+}
+
+#if defined(SELFTEST)
 #include <cstdio>
-#include <sys/time.h>
+#include "stopwatch.h"
+std::string s;
 int main()
 {
-	std::string s0 = string_format("%d_%d", 0, 1);
-	if (s0 != "0_1") {
-		printf("error\n");
-		return 1;
-	}
-	timeval start, end, result;
-	gettimeofday(&start, NULL);
-	for (int i = 0; i < 100000; i++) {
-		std::string s = string_format("%d_%d", i, i);
-	}
-	gettimeofday(&end, NULL);
-	timersub(&end, &start, &result);
-	long long t = (result.tv_sec) * 1000000 + result.tv_usec;
-	printf("%d.%03d\n", (int)t / 1000, (int)t % 1000);
+	Stopwatch sw;
+	sw.Start();
+	for (uint64 i = 0; i < 10000000; i += 3) {
+		s = format_number(i);
+		if (s.empty())
+			return 0;
+	}
+	sw.Stop();
+	uint64 t = sw.Elapsed();
+	printf("%ld.%03ld msec\n", t / 1000 / 1000, (t / 1000) % 1000);
 	return 0;
 }
 #endif