Make gcvt() better match printf("%g") behavior, it now passes regress.

OK deraadt@

1 files changed, 23 insertions, 11 deletions

diff --git a/src/lib/libc/stdlib/gcvt.c b/src/lib/libc/stdlib/gcvt.c
index e5488d912d..d9081a7d39 100644
--- a/src/lib/libc/stdlib/gcvt.c
+++ b/src/lib/libc/stdlib/gcvt.c
@@ -1,7 +1,8 @@
-/*      $OpenBSD: gcvt.c,v 1.11 2009/10/16 12:15:03 martynas Exp $      */
+/*      $OpenBSD: gcvt.c,v 1.12 2010/09/25 13:19:19 millert Exp $       */
 
 /*
- * Copyright (c) 2002, 2003, 2006 Todd C. Miller <Todd.Miller@courtesan.com>
+ * Copyright (c) 2002, 2003, 2006, 2010
+ *      Todd C. Miller <Todd.Miller@courtesan.com>
  *
  * Permission to use, copy, modify, and distribute this software for any
  * purpose with or without fee is hereby granted, provided that the above
@@ -28,6 +29,8 @@
 extern char *__dtoa(double, int, int, int *, int *, char **);
 extern void  __freedtoa(char *);
 
+#define DEFPREC 6
+
 char *
 gcvt(double value, int ndigit, char *buf)
 {
@@ -36,9 +39,9 @@ gcvt(double value, int ndigit, char *buf)
         struct lconv *lconv;
 
         lconv = localeconv();
-        if (ndigit == 0) {
-                buf[0] = '\0';
-                return (buf);
+        if (ndigit <= 0) {
+                /* Match printf(3) behavior. */
+                ndigit = ndigit ? DEFPREC : 1;
         }
 
         digits = __dtoa(value, 2, ndigit, &decpt, &sign, NULL);
@@ -47,9 +50,10 @@ gcvt(double value, int ndigit, char *buf)
         if (decpt == 9999) {
                 /*
                  * Infinity or NaN, convert to inf or nan with sign.
-                 * We assume the buffer is at least ndigit long.
+                 * We can't infer buffer size based on ndigit.
+                 * We have to assume it is at least 5 chars.
                  */
-                snprintf(buf, ndigit + 1, "%s%s", sign ? "-" : "",
+                snprintf(buf, 5, "%s%s", sign ? "-" : "",
                     *digits == 'I' ? "inf" : "nan");
                 __freedtoa(digits);
                 return (buf);
@@ -59,7 +63,8 @@ gcvt(double value, int ndigit, char *buf)
         if (sign)
                 *dst++ = '-';
 
-        if (decpt < 0 || decpt > ndigit) {
+        /* Match printf(3) behavior for exponential vs. regular fomatting. */
+        if (decpt <= -4 || decpt > ndigit) {
                 /* exponential format (e.g. 1.2345e+13) */
                 if (--decpt < 0) {
                         sign = 1;
@@ -68,9 +73,12 @@ gcvt(double value, int ndigit, char *buf)
                         sign = 0;
                 src = digits;
                 *dst++ = *src++;
-                *dst++ = *lconv->decimal_point;
-                while (*src != '\0')
-                        *dst++ = *src++;
+                if (*src != '\0') {
+                        *dst++ = *lconv->decimal_point;
+                        do {
+                                *dst++ = *src++;
+                        } while (*src != '\0');
+                }
                 *dst++ = 'e';
                 if (sign)
                         *dst++ = '-';
@@ -102,6 +110,10 @@ gcvt(double value, int ndigit, char *buf)
                         if (src == digits)
                                 *dst++ = '0';   /* zero before decimal point */
                         *dst++ = *lconv->decimal_point;
+                        while (decpt < 0) {
+                                *dst++ = '0';
+                                decpt++;
+                        }
                         for (i = decpt; digits[i] != '\0'; i++) {
                                 *dst++ = digits[i];
                         }