tjTrans: Allow 8x8 crop alignmnt w/odd 4:4:4 JPEGs

Fixes #549

ChangeLog.md

@@ -11,6 +11,11 @@ automatically place the `.rodata` section in an executable segment, which
 prevented libjpeg-turbo from working properly with other linkers and also
 represented a potential security risk.
 
+2. Fixed an issue whereby the `tjTransform()` function incorrectly computed the
+MCU block size for 4:4:4 JPEG images with non-unary sampling factors and thus
+unduly rejected some cropping regions, even though those regions aligned with
+8x8 MCU block boundaries.
+
 
 2.1.1
 =====

turbojpeg.c

@@ -1966,12 +1966,12 @@ DLLEXPORT int tjTransform(tjhandle handle, const unsigned char *jpegBuf,
       THROW("tjTransform(): Transform is not perfect");
 
     if (xinfo[i].crop) {
-      if ((t[i].r.x % xinfo[i].iMCU_sample_width) != 0 ||
-          (t[i].r.y % xinfo[i].iMCU_sample_height) != 0) {
+      if ((t[i].r.x % tjMCUWidth[jpegSubsamp]) != 0 ||
+          (t[i].r.y % tjMCUHeight[jpegSubsamp]) != 0) {
         snprintf(this->errStr, JMSG_LENGTH_MAX,
                  "To crop this JPEG image, x must be a multiple of %d\n"
                  "and y must be a multiple of %d.\n",
-                 xinfo[i].iMCU_sample_width, xinfo[i].iMCU_sample_height);
+                 tjMCUWidth[jpegSubsamp], tjMCUHeight[jpegSubsamp]);
         this->isInstanceError = TRUE;
         retval = -1;  goto bailout;
       }