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diff --git a/src/global/off_cvt.c b/src/global/off_cvt.c
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+/*++
+/* NAME
+/* off_cvt 3
+/* SUMMARY
+/* off_t conversions
+/* SYNOPSIS
+/* #include <off_cvt.h>
+/*
+/* off_t off_cvt_string(string)
+/* const char *string;
+/*
+/* VSTRING *off_cvt_number(result, offset)
+/* VSTRING *result;
+/* off_t offset;
+/* DESCRIPTION
+/* This module provides conversions between \fIoff_t\fR and string.
+/*
+/* off_cvt_string() converts a string, containing a non-negative
+/* offset, to numerical form. The result is -1 in case of problems.
+/*
+/* off_cvt_number() converts a non-negative offset to string form.
+/*
+/* Arguments:
+/* .IP string
+/* String with non-negative number to be converted to off_t.
+/* .IP result
+/* Buffer for storage of the result of conversion to string.
+/* .IP offset
+/* Non-negative off_t value to be converted to string.
+/* DIAGNOSTICS
+/* Panic: negative offset
+/* LICENSE
+/* .ad
+/* .fi
+/* The Secure Mailer license must be distributed with this software.
+/* AUTHOR(S)
+/* Wietse Venema
+/* IBM T.J. Watson Research
+/* P.O. Box 704
+/* Yorktown Heights, NY 10598, USA
+/*
+/* Wietse Venema
+/* Google, Inc.
+/* 111 8th Avenue
+/* New York, NY 10011, USA
+/*--*/
+
+/* System library. */
+
+#include <sys_defs.h>
+#include <sys/types.h>
+#include <ctype.h>
+
+/* Utility library. */
+
+#include <msg.h>
+#include <vstring.h>
+
+/* Global library. */
+
+#include "off_cvt.h"
+
+/* Application-specific. */
+
+#define STR vstring_str
+#define END vstring_end
+#define SWAP(type, a, b) { type temp; temp = a; a = b; b = temp; }
+
+/* off_cvt_string - string to number */
+
+off_t off_cvt_string(const char *str)
+{
+ int ch;
+ off_t result;
+ off_t digit_value;
+
+ /*
+ * Detect overflow before it happens. Code that attempts to detect
+ * overflow after-the-fact makes assumptions about undefined behavior.
+ * Compilers may invalidate such assumptions.
+ */
+ for (result = 0; (ch = *(unsigned char *) str) != 0; str++) {
+ if (!ISDIGIT(ch))
+ return (-1);
+ digit_value = ch - '0';
+ if (result > OFF_T_MAX / 10
+ || (result *= 10) > OFF_T_MAX - digit_value)
+ return (-1);
+ result += digit_value;
+ }
+ return (result);
+}
+
+/* off_cvt_number - number to string */
+
+VSTRING *off_cvt_number(VSTRING *buf, off_t offset)
+{
+ static char digs[] = "0123456789";
+ char *start;
+ char *last;
+ int i;
+
+ /*
+ * Sanity checks
+ */
+ if (offset < 0)
+ msg_panic("off_cvt_number: negative offset -%s",
+ STR(off_cvt_number(buf, -offset)));
+
+ /*
+ * First accumulate the result, backwards.
+ */
+ VSTRING_RESET(buf);
+ while (offset != 0) {
+ VSTRING_ADDCH(buf, digs[offset % 10]);
+ offset /= 10;
+ }
+ VSTRING_TERMINATE(buf);
+
+ /*
+ * Then, reverse the result.
+ */
+ start = STR(buf);
+ last = END(buf) - 1;
+ for (i = 0; i < VSTRING_LEN(buf) / 2; i++)
+ SWAP(int, start[i], last[-i]);
+ return (buf);
+}
+
+#ifdef TEST
+
+ /*
+ * Proof-of-concept test program. Read a number from stdin, convert to
+ * off_t, back to string, and print the result.
+ */
+#include <vstream.h>
+#include <vstring_vstream.h>
+
+int main(int unused_argc, char **unused_argv)
+{
+ VSTRING *buf = vstring_alloc(100);
+ off_t offset;
+
+ while (vstring_fgets_nonl(buf, VSTREAM_IN)) {
+ if (STR(buf)[0] == '#' || STR(buf)[0] == 0)
+ continue;
+ if ((offset = off_cvt_string(STR(buf))) < 0) {
+ msg_warn("bad input %s", STR(buf));
+ } else {
+ vstream_printf("%s\n", STR(off_cvt_number(buf, offset)));
+ }
+ vstream_fflush(VSTREAM_OUT);
+ }
+ vstring_free(buf);
+ return (0);
+}
+
+#endif