CFTimeZone: name and abbreviate GMT offsets like Apple

Source/CFTimeZone.c

@@ -306,11 +306,29 @@ CFTimeZoneCreateWithTimeIntervalFromGMT (CFAllocatorRef alloc,
   tzfile.header.tzh_timecnt[3] = 1;
   tzfile.header.tzh_typecnt[3] = 1;
   tzfile.ttinfo.offset = CFSwapInt32HostToBig((SInt32)ti);
-  numChars = snprintf (tzfile.abbrev, 10, "GMT%c%02d:%02d", sign, hour, min);
-  tzfile.header.tzh_charcnt[3] = numChars;
-
-  name = CFStringCreateWithCString (alloc, tzfile.abbrev,
-                                    kCFStringEncodingASCII);
+  /* The abbreviation is compact (GMT+5, GMT+5:30) while the name is padded
+     to four digits (GMT+0500).  A zero offset is just GMT. */
+  {
+    char nameBuf[16];
+
+    if ((SInt32) ti == 0)
+      {
+        numChars = snprintf (tzfile.abbrev, 10, "GMT");
+        snprintf (nameBuf, sizeof (nameBuf), "GMT");
+      }
+    else
+      {
+        if (min == 0)
+          numChars = snprintf (tzfile.abbrev, 10, "GMT%c%d", sign, hour);
+        else
+          numChars = snprintf (tzfile.abbrev, 10, "GMT%c%d:%02d",
+            sign, hour, min);
+        snprintf (nameBuf, sizeof (nameBuf), "GMT%c%02d%02d", sign, hour, min);
+      }
+    tzfile.header.tzh_charcnt[3] = numChars;
+
+    name = CFStringCreateWithCString (alloc, nameBuf, kCFStringEncodingASCII);
+  }
   data = CFDataCreateWithBytesNoCopy (alloc, (UInt8*)&tzfile,
     sizeof(struct TZFile) - (10 - numChars), kCFAllocatorNull);
   new = CFTimeZoneCreate (alloc, name, data);

Tests/CFTimeZone/basic.m

@@ -9,21 +9,16 @@ int main (void)
 {
   CFTimeZoneRef tz;
   CFStringRef str;
-  CFStringRef expected;
   CFTimeInterval ti;
   CFAbsoluteTime at;
 
   tz = CFTimeZoneCreateWithTimeIntervalFromGMT (NULL, 0.0);
   PASS_CF(tz != NULL, "CFTimeZone create successfully.");
-#ifdef __APPLE__
-  expected = CFSTR("GMT");
-#else
-  expected = CFSTR("GMT+00:00");
-#endif
-  PASS_CFEQ(CFTimeZoneGetName(tz), expected, "CFTimeZone has correct name.");
-
+  PASS_CFEQ(CFTimeZoneGetName(tz), CFSTR("GMT"),
+    "CFTimeZone has correct name.");
+
   str = CFTimeZoneCopyAbbreviation (tz, 0.0);
-  PASS_CFEQ(str, expected, "Time zone abbreviations are equal.");
+  PASS_CFEQ(str, CFSTR("GMT"), "Time zone abbreviations are equal.");
 
   ti = CFTimeZoneGetSecondsFromGMT (tz, 0.0);
   PASS_CF(ti == 0.0, "GMT+00:00 offset from GMT is %g", ti);

Tests/CFTimeZone/gmt_name.m

@@ -0,0 +1,70 @@
+#include "CoreFoundation/CFTimeZone.h"
+#include "../CFTesting.h"
+
+/* The name of a GMT-offset zone is GMT for a zero offset and GMT followed by
+   the signed four-digit offset otherwise; the abbreviation is compact. */
+
+static CFStringRef
+tzname_of (CFTimeInterval ti)
+{
+  CFTimeZoneRef tz = CFTimeZoneCreateWithTimeIntervalFromGMT (NULL, ti);
+  CFStringRef name = (CFStringRef) CFRetain (CFTimeZoneGetName (tz));
+  CFRelease (tz);
+  return name;
+}
+
+static CFStringRef
+tzabbr_of (CFTimeInterval ti)
+{
+  CFTimeZoneRef tz = CFTimeZoneCreateWithTimeIntervalFromGMT (NULL, ti);
+  CFStringRef abbr = CFTimeZoneCopyAbbreviation (tz, 0.0);
+  CFRelease (tz);
+  return abbr;
+}
+
+int main (void)
+{
+  CFStringRef s;
+
+  s = tzname_of (0.0);
+  PASS_CFEQ (s, CFSTR ("GMT"), "A zero offset is named GMT.");
+  CFRelease (s);
+  s = tzname_of (5 * 3600);
+  PASS_CFEQ (s, CFSTR ("GMT+0500"), "A five-hour offset is named GMT+0500.");
+  CFRelease (s);
+  s = tzname_of (-5 * 3600);
+  PASS_CFEQ (s, CFSTR ("GMT-0500"),
+    "A negative five-hour offset is named GMT-0500.");
+  CFRelease (s);
+  s = tzname_of (5 * 3600 + 30 * 60);
+  PASS_CFEQ (s, CFSTR ("GMT+0530"),
+    "A five-and-a-half-hour offset is named GMT+0530.");
+  CFRelease (s);
+  s = tzname_of (30 * 60);
+  PASS_CFEQ (s, CFSTR ("GMT+0030"), "A thirty-minute offset is named GMT+0030.");
+  CFRelease (s);
+
+  s = tzabbr_of (0.0);
+  PASS_CFEQ (s, CFSTR ("GMT"), "A zero offset abbreviates to GMT.");
+  CFRelease (s);
+  s = tzabbr_of (5 * 3600);
+  PASS_CFEQ (s, CFSTR ("GMT+5"), "A five-hour offset abbreviates to GMT+5.");
+  CFRelease (s);
+  s = tzabbr_of (-5 * 3600);
+  PASS_CFEQ (s, CFSTR ("GMT-5"),
+    "A negative five-hour offset abbreviates to GMT-5.");
+  CFRelease (s);
+  s = tzabbr_of (5 * 3600 + 30 * 60);
+  PASS_CFEQ (s, CFSTR ("GMT+5:30"),
+    "A five-and-a-half-hour offset abbreviates to GMT+5:30.");
+  CFRelease (s);
+  s = tzabbr_of (30 * 60);
+  PASS_CFEQ (s, CFSTR ("GMT+0:30"),
+    "A thirty-minute offset abbreviates to GMT+0:30.");
+  CFRelease (s);
+  s = tzabbr_of (10 * 3600);
+  PASS_CFEQ (s, CFSTR ("GMT+10"), "A ten-hour offset abbreviates to GMT+10.");
+  CFRelease (s);
+
+  return 0;
+}