Util::Str::group_digits -- readable msat/sat amounts in the xrebalance logs

Large amounts in the XRebalancer / XMoveFunds log lines were
unbroken digit runs (delivered 18851040 msat); grep-heavy log
sessions kept miscounting them.  Add Util::Str::group_digits,
which renders an integer with an underscore every three digit
places (18_851_040), matching the digit grouping
clboss-xrebalance-view and the other contrib tools already
print.

Applied to the amounts that get large:
- XRebalancer cycle line (derived N, request)
- XRebalancer transfer-done line (delivered, fee)
- XMoveFunds planning line (amount, maxfee)
- XMoveFunds 204 summary and fee-picture diagnostics
  (alloc_fee, required_out)
- XMoveFunds per-part budget refusals (would deliver)
- format_route_fees per-hop table (in/out/fee)

Counts, ppm values, and cltv deltas stay plain.  Signed
overload handles the int64 call sites (INT64_MIN-safe).

New tests/util/test_str covers both overloads and the
boundary cases.

Boss/Mod/XMoveFunds/Main.cpp

@@ -285,8 +285,10 @@ format_route_fees(Jsmn::Object const& path) {
 		auto cout = hop.has("cltv_out")
 			  ? std::uint32_t(double(hop["cltv_out"])) : 0u;
 		os << "  [" << i << "] " << scidd
-		   << " in=" << ain << " out=" << aout
-		   << " fee=" << fee << "msat(" << ppm << "ppm)"
+		   << " in=" << Util::Str::group_digits(ain)
+		   << " out=" << Util::Str::group_digits(aout)
+		   << " fee=" << Util::Str::group_digits(fee)
+		   << "msat(" << ppm << "ppm)"
 		   << " cltv " << cin << "->" << cout
 		   << " d=" << (cin >= cout ? cin - cout : 0u) << "\n";
 	}
@@ -1215,7 +1217,9 @@ private:
 				    << std::dec << " erring=" << echan_str << "/" << edir
 				    << " node=" << std::string(enode)
 				    << " from_target=" << from_target
-				    << " alloc_fee=" << alloc << "msat";
+				    << " alloc_fee="
+				    << Util::Str::group_digits(alloc)
+				    << "msat";
 				ChanUpdate scu;
 				if (data.has("raw_message")
 				 && eidx < askrene_path.size()
@@ -1227,7 +1231,9 @@ private:
 					auto req_out = std::uint64_t(scu.fee_base_msat)
 					    + std::uint64_t(scu.fee_proportional_millionths)
 					      * out / 1000000;
-					sum << " required_out=" << req_out << "msat";
+					sum << " required_out="
+					    << Util::Str::group_digits(req_out)
+					    << "msat";
 					if (scu.has_inbound_fee)
 						sum << " inbound_ppm="
 						    << scu.inbound_fee_proportional_millionths;
@@ -1265,7 +1271,8 @@ private:
 					auto alloc = (in >= out) ? in - out
 						   : std::uint64_t(0);
 					os << "  erring hop[" << eidx
-					   << "] allocated fee=" << alloc
+					   << "] allocated fee="
+					   << Util::Str::group_digits(alloc)
 					   << "msat\n";
 					if (data.has("raw_message")) {
 						ChanUpdate dcu;
@@ -1285,7 +1292,10 @@ private:
 							   << " out_ppm="
 							   << dcu.fee_proportional_millionths
 							   << " -> required_out="
-							   << req_out << "msat";
+							   << Util::Str::
+								group_digits(
+								    req_out)
+							   << "msat";
 							if (dcu.has_inbound_fee)
 								os << "; inbound_base="
 								   << dcu.inbound_fee_base_msat
@@ -1784,10 +1794,12 @@ private:
 							  "refused: %.0f ppm "
 							  "exceeds budget %.0f "
 							  "ppm (would deliver "
-							  "%" PRIu64 " msat)"
+							  "%s msat)"
 							, i, part_ppm
 							, budget_ppm
-							, deliv_msat );
+							, Util::Str::group_digits(
+								deliv_msat)
+							    .c_str() );
 						continue;
 					}
 				}
@@ -2265,13 +2277,15 @@ private:
 
 		return Boss::log( bus, Info
 				, "XMoveFunds: planning %s -> %s, "
-				  "amount=%" PRIu64 " msat, "
-				  "maxfee=%" PRIu64 " msat, "
+				  "amount=%s msat, "
+				  "maxfee=%s msat, "
 				  "maxparts=%" PRIu32 ", execute=%s"
 				, join_scids(p->source_scids).c_str()
 				, join_scids(p->dest_scids).c_str()
-				, std::uint64_t(p->amount.to_msat())
-				, std::uint64_t(p->maxfee.to_msat())
+				, Util::Str::group_digits(std::uint64_t(
+					p->amount.to_msat())).c_str()
+				, Util::Str::group_digits(std::uint64_t(
+					p->maxfee.to_msat())).c_str()
 				, p->maxparts
 				, p->execute ? "true" : "false"
 				)

Boss/Mod/XRebalancer.cpp

@@ -20,6 +20,7 @@
 #include"Ln/NodeId.hpp"
 #include"S/Bus.hpp"
 #include"Sqlite3.hpp"
+#include"Util/Str.hpp"
 #include"Util/make_unique.hpp"
 #include<algorithm>
 #include<ctime>
@@ -700,15 +701,18 @@ private:
 		return Boss::log( bus, Info, "%s", levels_str.c_str() )
 		     + Boss::log( bus, Info
 			, "XRebalancer: cycle [xrebalance] floor=%.1f%s window=%.0fd "
-			  "-> derived N=%lld sat, joint=%.1f ppm "
+			  "-> derived N=%s sat, joint=%.1f ppm "
 			  "(fill>=%.1f + drain>=%.1f); size_factor=%.3g%s "
-			  "-> request=%lld sat (maxfee %u ppm); "
+			  "-> request=%s sat (maxfee %u ppm); "
 			  "sources=%zu dests=%zu; executing."
 			, effective_floor, picked_note.c_str(), window_days
-			, (long long)best_n, best_joint
+			, Util::Str::group_digits(
+				std::int64_t(best_n)).c_str(), best_joint
 			, best_fill_ppm, best_drain_ppm
 			, effective_size_factor, sf_note.c_str()
-			, (long long)requested, (unsigned)maxfee
+			, Util::Str::group_digits(
+				std::int64_t(requested)).c_str()
+			, (unsigned)maxfee
 			, source_scids.size(), dest_scids.size()
 			).then([this, source_scids, dest_scids]() {
 			return Boss::log( bus, Debug
@@ -860,9 +864,15 @@ private:
 			 * economics; reason is present only on a partial.  */
 			return Boss::log( bus, Info
 				, "XRebalancer: transfer done: %.0f/%.0f parts, "
-				  "delivered %.0f msat, fee %.0f msat%s%s."
+				  "delivered %s msat, fee %s msat%s%s."
 				, num("parts_complete"), num("parts")
-				, delivered, fee, ppm.c_str(), reason.c_str() );
+				, Util::Str::group_digits(
+					std::int64_t(std::llround(
+						delivered))).c_str()
+				, Util::Str::group_digits(
+					std::int64_t(std::llround(
+						fee))).c_str()
+				, ppm.c_str(), reason.c_str() );
 		/* Nothing delivered: a clean failure -- show the part count
 		 * attempted and the chokepoint, not three zeros.  */
 		return Boss::log( bus, Info

Makefile.am

@@ -699,7 +699,8 @@ TESTS = \
 	tests/util/test_date \
 	tests/util/test_duration \
 	tests/util/test_either \
-	tests/util/test_format
+	tests/util/test_format \
+	tests/util/test_str
 check_PROGRAMS = $(TESTS)
 
 if USE_VALGRIND

Util/Str.cpp

@@ -92,6 +92,25 @@ std::string trim(std::string const& s) {
 	return std::string(start, end);
 }
 
+std::string group_digits(std::uint64_t v) {
+	auto s = std::to_string(v);
+	auto out = std::string();
+	auto n = s.size();
+	for (auto i = std::size_t(0); i < n; ++i) {
+		if (i != 0 && (n - i) % 3 == 0)
+			out += '_';
+		out += s[i];
+	}
+	return out;
+}
+
+std::string group_digits(std::int64_t v) {
+	if (v < 0)
+		/* -(v + 1) is representable even for INT64_MIN.  */
+		return "-" + group_digits(std::uint64_t(-(v + 1)) + 1);
+	return group_digits(std::uint64_t(v));
+}
+
 std::string fmt(char const *tpl, ...) {
 	va_list ap;
 

Util/Str.hpp

@@ -34,6 +34,13 @@ bool ishex(std::string const&);
 
 std::string trim(std::string const& s);
 
+/* Renders an integer with '_' between every three digit places
+ * (18851040 -> "18_851_040"), for log lines carrying large msat/sat
+ * amounts.  Matches the digit grouping clboss-xrebalance-view and
+ * the other contrib tools print.  */
+std::string group_digits(std::uint64_t);
+std::string group_digits(std::int64_t);
+
 /* Like `sprintf`.  */
 std::string fmt(char const *tpl, ...)
 #if HAVE_ATTRIBUTE_FORMAT

tests/util/test_str.cpp

@@ -0,0 +1,25 @@
+#undef NDEBUG
+#include"Util/Str.hpp"
+#include<assert.h>
+#include<cstdint>
+
+int main() {
+	using Util::Str::group_digits;
+
+	/* Unsigned.  */
+	assert(group_digits(std::uint64_t(0)) == "0");
+	assert(group_digits(std::uint64_t(999)) == "999");
+	assert(group_digits(std::uint64_t(1000)) == "1_000");
+	assert(group_digits(std::uint64_t(18851040)) == "18_851_040");
+	assert(group_digits(std::uint64_t(220708066)) == "220_708_066");
+	assert( group_digits(std::uint64_t(18446744073709551615ull))
+	     == "18_446_744_073_709_551_615");
+
+	/* Signed.  */
+	assert(group_digits(std::int64_t(-1)) == "-1");
+	assert(group_digits(std::int64_t(-18851040)) == "-18_851_040");
+	assert( group_digits(std::int64_t(INT64_MIN))
+	     == "-9_223_372_036_854_775_808");
+
+	return 0;
+}