From fc0c76a075b462ec0c01540536949c6db1308aee Mon Sep 17 00:00:00 2001
From: Victor Zverovich <viz@meta.com>
Date: Sun, 1 Jun 2025 08:26:53 -0700
Subject: [PATCH] Handle large precision

---
 include/fmt/format.h |  4 ++--
 test/format-test.cc  | 29 ++++++++++++++++++++++++++---
 2 files changed, 28 insertions(+), 5 deletions(-)

diff --git a/include/fmt/format.h b/include/fmt/format.h
index 90fe56d7..beb81885 100644
--- a/include/fmt/format.h
+++ b/include/fmt/format.h
@@ -2392,7 +2392,7 @@ FMT_CONSTEXPR20 auto write_fixed(OutputIt out, const DecimalFP& f,
   using iterator = reserve_iterator<OutputIt>;
 
   int exp = f.exponent + significand_size;
-  int size = significand_size + (s != sign::none ? 1 : 0);
+  long long size = significand_size + (s != sign::none ? 1 : 0);
   if (f.exponent >= 0) {
     // 1234e5 -> 123400000[.0+]
     size += f.exponent;
@@ -2466,7 +2466,7 @@ FMT_CONSTEXPR20 auto do_write_float(OutputIt out, const DecimalFP& f,
 
   // Write value in the exponential format.
   int num_zeros = 0;
-  int size = significand_size + (s != sign::none ? 1 : 0);
+  long long size = significand_size + (s != sign::none ? 1 : 0);
   if (specs.alt()) {
     num_zeros = max_of(specs.precision - significand_size, 0);
     size += num_zeros;
diff --git a/test/format-test.cc b/test/format-test.cc
index c0e1ea68..124b9bd2 100644
--- a/test/format-test.cc
+++ b/test/format-test.cc
@@ -1095,9 +1095,6 @@ TEST(format_test, precision) {
   EXPECT_THROW_MSG(
       (void)fmt::format(runtime("{0:.2f}"), reinterpret_cast<void*>(0xcafe)),
       format_error, "invalid format specifier");
-  EXPECT_THROW_MSG((void)fmt::format(runtime("{:.{}e}"), 42.0,
-                                     fmt::detail::max_value<int>()),
-                   format_error, "number is too big");
   EXPECT_THROW_MSG(
       (void)fmt::format("{:.2147483646f}", -2.2121295195081227E+304),
       format_error, "number is too big");
@@ -1109,6 +1106,32 @@ TEST(format_test, precision) {
   EXPECT_EQ(fmt::format("{0:.6}", "123456\xad"), "123456");
 }
 
+TEST(format_test, large_precision) {
+  // Iterator used to abort the actual output.
+  struct throwing_iterator {
+    auto operator=(char) -> throwing_iterator& {
+      throw std::runtime_error("aborted");
+      return *this;
+    }
+    auto operator*() -> throwing_iterator& { return *this; }
+    auto operator++() -> throwing_iterator& { return *this; }
+    auto operator++(int) -> throwing_iterator { return *this; }
+  };
+  auto it = throwing_iterator();
+
+  EXPECT_THROW_MSG(fmt::format_to(it, fmt::runtime("{:#.{}}"), 1.0,
+                                  fmt::detail::max_value<int>()),
+                   std::runtime_error, "aborted");
+
+  EXPECT_THROW_MSG(fmt::format_to(it, fmt::runtime("{:#.{}e}"), 1.0,
+                                  fmt::detail::max_value<int>() - 1),
+                   std::runtime_error, "aborted");
+
+  EXPECT_THROW_MSG((void)fmt::format(fmt::runtime("{:.{}e}"), 42.0,
+                                     fmt::detail::max_value<int>()),
+                   format_error, "number is too big");
+}
+
 TEST(format_test, utf8_precision) {
   auto result = fmt::format("{:.4}", "caf\u00e9s");  // cafés
   EXPECT_EQ(fmt::detail::compute_width(result), 4);