[RFC weston] Add strtoint() helper

[Bryce Harrington]

Adds a safe strtol helper function, modeled loosely after Wayland
scanner's strtouint.  This encapsulates the various quirks of strtol
behavior, and streamlines the interface to just handling base-10 numbers
with a simple true/false error indicator.

Signed-off-by: Bryce Harrington <bryce at osg.samsung.com>
---

Hi,

With much of the strtol uses cleaned up, I figure the time's ripe to
introduce a helper routine for factoring the logic out.

For brevity I've omitted tests and the actual substitution of this
routine into the codebase - those should be straightforward once the
function implementation is deemed acceptable and I plan to add them.

The implementation style is derived from Wayland scanner's strtouint.
Placement of the code as an inline function in its own shared header
file is following the precident set with shared/zalloc.h.  Both of these
are just arbitrary choices though.

The most notable difference from strtouint() is that the value is
returned by reference rather than as a return value.  This approach
was suggested originally by Peter Hutterer, and is felt to provide
a more reliably robust error handling mechanism.

So, some questions I'm requesting comment on:

1. Is 'strtoint' an ok name for the function?  What would be better?

2. I plan to also add similar helpers for uint and hexadecimal (color)
   parsing.  Should a more general filename be chosen than strtoint.h?

3. Do we care at all about detailed error codes (ERANGE or EINVAL)?
   This implementation assumes 'no', which is based on the lack of use
   of detailed errno checks in the current codebase.

4. Should the return data type be int or int32_t?  I've seen it both
   ways through the code.  I picked int here just since that's what
   scanner.c uses.   

5. Is it appropriate for this function to be inline in a header like
   done with zalloc, or should the implementation be in a .c file
   like done with most of the other helper routines?

 shared/strtoint.h | 72 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 72 insertions(+)
 create mode 100644 shared/strtoint.h

diff --git a/shared/strtoint.h b/shared/strtoint.h
new file mode 100644
index 0000000..c4d2928
--- /dev/null
+++ b/shared/strtoint.h
@@ -0,0 +1,72 @@
+/*
+ * Copyright © 2015 Samsung Electronics Co., Ltd
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the
+ * next paragraph) shall be included in all copies or substantial
+ * portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT.  IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+ * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+ * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+#ifndef WESTON_STRTOINT_H
+#define WESTON_STRTOINT_H
+
+#ifdef  __cplusplus
+extern "C" {
+#endif
+
+#include <errno.h>
+
+/* Convert string to integer
+ *
+ * Parses a base-10 number from the given string.  Checks that the
+ * string is not blank, contains only numerical characters, and is
+ * within the range of -INT_MAX to INT_MAX.  If the validation is
+ * successful the result is stored in *value.
+ *
+ * Upon error, this routine does not modify or set errno, and leaves
+ * *value unchanged.
+ *
+ * \returns true if number parsed successfully, false on error
+ */
+static inline bool
+strtoint(const char *str, int *value)
+{
+	int ret;
+	char *end;
+	int prev_errno = errno;
+
+	errno = 0;
+	ret = strtol(str, &end, 10);
+
+	if (errno != 0 || end == str || *end != '\0') {
+		errno = prev_errno;
+		return false;
+	}
+
+	*value = ret;
+	errno = prev_errno;
+
+	return true;
+}
+
+#ifdef  __cplusplus
+}
+#endif
+
+#endif /* WESTON_STRTOINT_H */
-- 
1.9.1