From de48f75e96829aab422eda963f684b30bd0eba54 Mon Sep 17 00:00:00 2001
From: Danny Robson <danny@nerdcruft.net>
Date: Wed, 10 Aug 2016 17:38:39 +1000
Subject: [PATCH] format: fix transcription of zero values to strings

an iteration condition terminated the write when a value was zero rather
than when all numerals were written. instead, iterate over the remaining
numerals.

fixes printf("%zu", 0u)
---
 format.ipp      | 7 +++++--
 test/format.cpp | 1 +
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/format.ipp b/format.ipp
index fa5cbbb4..7bbdd219 100644
--- a/format.ipp
+++ b/format.ipp
@@ -743,6 +743,7 @@ namespace util { namespace format { namespace detail {
 
         const auto numerals   = digits (t, spec.base);
         const auto characters = numerals + (spec.positive_char ? 1 : 0);
+        CHECK_NEZ (numerals);
 
         // add any requested positive signifier
         if (spec.positive_char)
@@ -775,11 +776,13 @@ namespace util { namespace format { namespace detail {
         // output is blank (though space padding/etc is still preserved).
         if (t != 0 || spec.precision != 0) {
             const char *NUMERALS = spec.uppercase ?
-                "0123456789ABCDEF" :
+                "0123456789ABCDEF":
                 "0123456789abcdef";
 
             char buffer[numerals];
-            for (auto cursor = buffer; t; t /= spec.base)
+            size_t remain = numerals;
+
+            for (auto cursor = buffer; remain--; t /= spec.base)
                 *cursor++ = NUMERALS[t % spec.base];
             std::reverse_copy (buffer, buffer + numerals, os);
         }
diff --git a/test/format.cpp b/test/format.cpp
index 4ecf9697..97564b72 100644
--- a/test/format.cpp
+++ b/test/format.cpp
@@ -53,6 +53,7 @@ main (void)
     CHECK_RENDER ("%lu", "1",  (unsigned long)1);
     CHECK_RENDER ("%llu", "1", (unsigned long long)1);
     CHECK_RENDER ("%ju", "1",  (uintmax_t)1);
+    CHECK_RENDER ("%zu", "0",  (size_t)0);
     CHECK_RENDER ("%zu", "1",  (size_t)1);
 
     CHECK_RENDER ("%o", "1", 01u);