From 792b1c84c0f2810ada230eff3a857ce7ce0ce6a4 Mon Sep 17 00:00:00 2001
From: Gabriel Ravier <gabravier@gmail.com>
Date: Sat, 25 Mar 2023 19:39:25 +0100
Subject: [PATCH] Fix padding+minus flag on numbers for printf-family functions
 (#787)

The C standard states, for conversions using the d, i, b, B, o, u, x or X conversion specifiers:
> The precision specifies the minimum number of digits to appear; if
> the value being converted can be represented in fewer digits, it is
> expanded with leading zeros.
- C standard, 7.23.6.1. The fprintf function

However, cosmopolitan currently suppresses the addition of leading
zeros when the minus flag is set. This is not reflected by anything
within the C standard, meaning that behavior is incorrect.

This patch fixes this.
---
 libc/fmt/ntoa.c          | 24 +++++++++++-------------
 test/libc/fmt/fmt_test.c | 19 +++++++++++++++++++
 2 files changed, 30 insertions(+), 13 deletions(-)

diff --git a/libc/fmt/ntoa.c b/libc/fmt/ntoa.c
index 8bf081768..8b1878df0 100644
--- a/libc/fmt/ntoa.c
+++ b/libc/fmt/ntoa.c
@@ -34,17 +34,15 @@ static int __fmt_ntoa_format(int out(const char *, void *, size_t), void *arg,
                              unsigned char flags) {
   unsigned i;
   /* pad leading zeros */
-  if (!(flags & FLAGS_LEFT)) {
-    if (width && (flags & FLAGS_ZEROPAD) &&
-        (negative || (flags & (FLAGS_PLUS | FLAGS_SPACE)))) {
-      width--;
-    }
-    while ((len < prec) && (len < BUFFER_SIZE)) {
-      buf[len++] = '0';
-    }
-    while ((flags & FLAGS_ZEROPAD) && (len < width) && (len < BUFFER_SIZE)) {
-      buf[len++] = '0';
-    }
+  if (width && (flags & FLAGS_ZEROPAD) &&
+      (negative || (flags & (FLAGS_PLUS | FLAGS_SPACE)))) {
+    width--;
+  }
+  while ((len < prec) && (len < BUFFER_SIZE)) {
+    buf[len++] = '0';
+  }
+  while ((flags & FLAGS_ZEROPAD) && (len < width) && (len < BUFFER_SIZE)) {
+    buf[len++] = '0';
   }
   /* handle hash */
   if (flags & FLAGS_HASH) {
@@ -134,8 +132,8 @@ int __fmt_ntoa(int out(const char *, void *, size_t), void *arg, va_list va,
   bool neg;
   uint128_t value, sign;
 
-  /* ignore '0' flag when prec is given */
-  if (flags & FLAGS_PRECISION) {
+  /* ignore '0' flag when prec or minus flag is given */
+  if (flags & (FLAGS_PRECISION | FLAGS_LEFT)) {
     flags &= ~FLAGS_ZEROPAD;
   }
 
diff --git a/test/libc/fmt/fmt_test.c b/test/libc/fmt/fmt_test.c
index caef6f655..bccd22e9a 100644
--- a/test/libc/fmt/fmt_test.c
+++ b/test/libc/fmt/fmt_test.c
@@ -62,6 +62,25 @@ TEST(fmt, d) {
   EXPECT_STREQ(" 16", _gc(xasprintf("% d", 16)));
   EXPECT_STREQ(" 2147483647", _gc(xasprintf("% d", INT_MAX)));
   EXPECT_STREQ("-2147483648", _gc(xasprintf("% d", INT_MIN)));
+  EXPECT_STREQ("042 ", _gc(xasprintf("%-4.3d", 42)));
+  EXPECT_STREQ("-00054", _gc(xasprintf("%-1.5lld", -54ll)));
+  EXPECT_STREQ("00109", _gc(xasprintf("%-.5lld", 109ll)));
+  EXPECT_STREQ("-00116", _gc(xasprintf("%-.5lld", -116ll)));
+  EXPECT_STREQ("00108   ", _gc(xasprintf("%-8.5lld", 108ll)));
+  EXPECT_STREQ("-00054  ", _gc(xasprintf("%-8.5lld", -54ll)));
+}
+
+TEST(fmt, u) {
+  EXPECT_STREQ("042 ", _gc(xasprintf("%-4.3u", 42)));
+}
+
+TEST(fmt, x) {
+  EXPECT_STREQ("0x01   ", _gc(xasprintf("%#-07.2x", 1)));
+  EXPECT_STREQ("0x00136d  ", _gc(xasprintf("%#-010.6x", 4973)));
+}
+
+TEST(fmt, b) {
+  EXPECT_STREQ("000010100     ", _gc(xasprintf("%-14.9b", 20)));
 }
 
 TEST(fmt, s) {