From 44b65521e0e87f7979d2ed0cbf602be627737eb9 Mon Sep 17 00:00:00 2001
From: Ian Moffett <ian@osmora.org>
Date: Sun, 26 May 2024 23:32:22 -0400
Subject: kernel: string: Support '%0Nd' formatting

Signed-off-by: Ian Moffett <ian@osmora.org>
---
 sys/lib/string/vsnprintf.c | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

(limited to 'sys/lib/string')

diff --git a/sys/lib/string/vsnprintf.c b/sys/lib/string/vsnprintf.c
index 1468a11..b8a4faa 100644
--- a/sys/lib/string/vsnprintf.c
+++ b/sys/lib/string/vsnprintf.c
@@ -64,10 +64,11 @@ snprintf(char *s, size_t size, const char *fmt, ...)
 int
 vsnprintf(char *s, size_t size, const char *fmt, va_list ap)
 {
-    size_t tmp_len, off = 0;
+    size_t tmp_len, num_len, off = 0;
     ssize_t num = 0;
     char c, c1, num_buf[256] = {0};
     const char *tmp_str;
+    uint8_t pad_width = 0;
 
     while (off < (size - 1)) {
         while (*fmt && *fmt != '%') {
@@ -77,6 +78,18 @@ vsnprintf(char *s, size_t size, const char *fmt, va_list ap)
             return off;
         }
 
+        /*
+         * Handle a case where we have "%0N". For example:
+         * "%04d"
+         */
+        if (*fmt == '0') {
+            ++fmt;
+            while (*fmt >= '0' && *fmt <= '9') {
+                pad_width = pad_width * 10 + (*fmt - '0');
+                ++fmt;
+            }
+        }
+
         c = *fmt++;
         switch (c) {
         case 'c':
@@ -86,6 +99,12 @@ vsnprintf(char *s, size_t size, const char *fmt, va_list ap)
         case 'd':
             num = va_arg(ap, int);
             itoa(num, num_buf, 10);
+
+            if (pad_width > 0) {
+                num_len = strlen(num_buf);
+                for (size_t i = num_len; i < pad_width; ++i)
+                    printc(s, size, &off, '0');
+            }
             printstr(s, size, &off, num_buf);
             break;
         case 'p':
-- 
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