Re: [ft-devel] New Infinality Release

[Werner LEMBERG]

>> Have you actually done binary searches in TTFs to find signatures?
>
> Well, only using the code here, not with a hex editor.  I have seen
> hits in some TTF files where I would not have expected them.  May
> speak to the issues you mentioned below.

OK.  So it's definitely worth some tests :-)

>> [...] I think it is best if you extend the code so that the
>> function number is also checked to avoid false hits.
> 
> Yes, this makes sense for functions where we know the number, such
> as ttfautohint and 0.

Well, most of the bytecode snippets are associated with one or more
fixed function numbers.

> But, I think the whitepaper states that on (at least some)
> functions, the number varies, which is why you need the detection
> code in the first place.

Correct.  My concern is that we get false hits due to the shortness of
the snippets.

> Regarding the problems with the opcode patterns, what did you see
> that was incorrect?  From scanning them (quickly) it seemed like it
> was mostly correct (perhaps missing the end IF, etc.)

Ah, I see that I've done a mistake, below is a corrected patch
(untested).  However, I think that the current method is flawed in
general since arguments to opcodes are completely ignored by
`SKIP_Code'.  For example, it is not possible to decide whether the
bytecode is

  SVTCA_x
  PUSHB_1
    24
  RS
  IF

or

  SVTCA_x
  PUSHB_1
    39
  RS
  IF

It seems to me that we really have to compare the *complete* bytecode
(including the arguments) within `Ins_FDEF'.


    Werner

diff --git a/src/truetype/ttinterp.c b/src/truetype/ttinterp.c
index 505168d..ebd433c 100644
--- a/src/truetype/ttinterp.c
+++ b/src/truetype/ttinterp.c
@@ -4610,25 +4610,91 @@
     FT_ULong       n;
     TT_DefRecord*  rec;
     TT_DefRecord*  limit;
+
 #ifdef TT_CONFIG_OPTION_SUBPIXEL_HINTING
+    /* arguments to opcodes are skipped by `SKIP_Code' */
     FT_Byte    opcode_pattern[7][12] = {
-                 /* inline delta function 1 */
-                 {0x4B,0x53,0x23,0x4B,0x51,0x5A,0x58,0x38,0x1B,0x21,0x21,0x59},
-                 /* inline delta function 2 */
-                 {0x4B,0x54,0x58,0x38,0x1B,0x5A,0x21,0x21,0x59,},
-                 /* diagonal stroke function */
-                 {0x20,0x20,0x40,0x60,0x47,0x40,0x23,0x42,},
-                 /* VacuFormRound function */
-                 {0x45,0x23,0x46,0x60,0x20,},
-                 /* ttfautohinted */
-                 {0x20,0x64,0xb0,0x60,0x66,0x23,0xb0,},
-                 /* spacing functions */
-                 {0x01,0x41,0x43,0x58,},
-                 {0x01,0x18,0x41,0x43,0x58,},
+                 /* #0 inline delta function 1 */
+                 {
+                   0x4B, /* PPEM    */
+                   0x53, /* GTEQ    */
+                   0x23, /* SWAP    */
+                   0x4B, /* PPEM    */
+                   0x51, /* LTEQ    */
+                   0x5A, /* AND     */
+                   0x58, /* IF      */
+                   0x38, /*   SHPIX */
+                   0x1B, /* ELSE    */
+                   0x21, /*   POP   */
+                   0x21, /*   POP   */
+                   0x59  /* EIF     */
+                 },
+                 /* #1 inline delta function 2 */
+                 {
+                   0x4B, /* PPEM    */
+                   0x54, /* EQ      */
+                   0x58, /* IF      */
+                   0x38, /*   SHPIX */
+                   0x1B, /* ELSE    */
+                   0x21, /*   POP   */
+                   0x21, /*   POP   */
+                   0x59  /* EIF     */
+                 },
+                 /* #2 diagonal stroke function */
+                 {
+                   0x20, /* DUP     */
+                   0x20, /* DUP     */
+                   0xB0, /* PUSHB_1 */
+                         /*   1     */
+                   0x60, /* ADD     */
+                   0x46, /* GC_cur  */
+                   0xB0, /* PUSHB_1 */
+                         /*   64    */
+                   0x23, /* SWAP    */
+                   0x42  /* WS      */
+                 },
+                 /* #3 VacuFormRound function */
+                 {
+                   0x45, /* RCVT    */
+                   0x23, /* SWAP    */
+                   0x46, /* GC_cur  */
+                   0x60, /* ADD     */
+                   0x20, /* DUP     */
+                   0xB0  /* PUSHB_1 */
+                         /*   38    */
+                 },
+                 /* #4 TTFautohint bytecode (old) */
+                 {
+                   0x20, /* DUP     */
+                   0x64, /* ABS     */
+                   0xB0, /* PUSHB_1 */
+                         /*   32    */
+                   0x60, /* ADD     */
+                   0x66, /* FLOOR   */
+                   0x23, /* SWAP    */
+                   0xB0  /* PUSHB_1 */
+                 },
+                 /* #5 spacing function 1 */
+                 {
+                   0x01, /* SVTCA_x */
+                   0xB0, /* PUSHB_1 */
+                         /*   24    */
+                   0x43, /* RS      */
+                   0x58  /* IF      */
+                 },
+                 /* #6 spacing function 2 */
+                 {
+                   0x01, /* SVTCA_x */
+                   0x18, /* RTG     */
+                   0xB0, /* PUSHB_1 */
+                         /*   24    */
+                   0x43, /* RS      */
+                   0x58  /* IF      */
+                 },
                };
     FT_UShort  opcode_patterns   = 7;
-    FT_UShort  opcode_pointer[7] = {0,0,0,0,0,0,0};
-    FT_UShort  opcode_size[7]    = {12,9,8,5,7,4,5};
+    FT_UShort  opcode_pointer[7] = {  0, 0, 0, 0, 0, 0, 0 };
+    FT_UShort  opcode_size[7]    = { 12, 8, 8, 6, 7, 4, 5 };
     FT_UShort  i;
 #endif /* TT_CONFIG_OPTION_SUBPIXEL_HINTING */