usr: libc: Add atoi()

Signed-off-by: Ian Moffett <ian@osmora.org>

2 files changed, 52 insertions, 0 deletions

diff --git a/lib/libc/include/string.h b/lib/libc/include/string.h
index dcf25cc..4ac384b 100644
--- a/lib/libc/include/string.h
+++ b/lib/libc/include/string.h
@@ -40,5 +40,6 @@ int memcmp(const void *s1, const void *s2, size_t n);
 char *itoa(int64_t value, char *buf, int base);
 void *memcpy(void *dest, const void *src, size_t n);
 int strcmp(const char *s1, const char *s2);
+int atoi(char *s);
 
 #endif  /* !_STRING_H_ */
diff --git a/lib/libc/src/string/atoi.c b/lib/libc/src/string/atoi.c
new file mode 100644
index 0000000..24943da
--- /dev/null
+++ b/lib/libc/src/string/atoi.c
@@ -0,0 +1,51 @@
+/*
+ * Copyright (c) 2023-2025 Ian Marco Moffett and the Osmora Team.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of Hyra nor the names of its
+ *    contributors may be used to endorse or promote products derived from
+ *    this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <string.h>
+
+#define IS_DIGIT(C) ((C >= '0' && C <= '9'))
+
+int
+atoi(char *s)
+{
+    int n, sign;
+
+    while (*s == ' ') {
+        ++s;
+    }
+
+    sign = (*s == '-') ? -1 : 1;
+    if (*s == '+' || *s == '-') {
+        s++;
+    }
+    for (n = 0; IS_DIGIT(*s); ++s) {
+        n = 10 * n + (*s - '0');
+    }
+    return sign * n;
+}