[ft-devel] Question about TTF

[Zeming Liu]

Dear FreeType team,

     I am a grad student of University of Waterloo.  We have a project about TTF. We are trying to translate TTF bytecode to some kind of 3-addr-code, and optimize the 3-addr-code, then convert it back to bytecode.

     We tested our program on arial.ttf, and found that there is a CALL instruction in some fpgm, which calls an uncertain fixed point value( bytecode attached below ).

     As you can see, the callee is the result of a series of arithmetic operations, (  4096 DIV MIN(MAX(0, 64 SUB F26Dot6), 192) ADD 44 ), where 192 not even divides 4096.

     So, I wonder how do you deal with such a call instruction, do you just throw an exception?   There is very few documentation about ttf we can find, so your advice will be very helpful. I expect to here from you soon.

best wishes

Zeming

      PUSH[ ]
      17
      FDEF[ ]   /* FunctionDefinition */
      DUP[ ]    /* DuplicateTopStack */
      ROUND[01] /* Round */
      PUSHB[ ]  /* 1 value pushed */
      64
      SUB[ ]    /* Subtract */
      PUSHB[ ]  /* 1 value pushed */
      0
      MAX[ ]    /* Maximum */
      DUP[ ]    /* DuplicateTopStack */
      PUSHB[ ]  /* 2 values pushed */
      44  192
      ROLL[ ]   /* RollTopThreeStack */
      MIN[ ]    /* Minimum */
      PUSHW[ ]  /* 1 value pushed */
      4096 /* word */
      DIV[ ]    /* Divide */
      ADD[ ]    /* Add */
      CALL[ ]   /* CallFunction */
      GPV[ ]    /* GetPVector */
      ABS[ ]    /* Absolute */
      SWAP[ ]   /* SwapTopStack */
      ABS[ ]    /* Absolute */
      SUB[ ]    /* Subtract */
      NOT[ ]    /* LogicalNot */
      IF[ ]     /* If */
      PUSHB[ ]  /* 1 value pushed */
      3
      SUB[ ]    /* Subtract */
      EIF[ ]    /* EndIf */
      ENDF[ ]   /* EndFunctionDefinition */