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[cff] Fix Savannah bug #43271.

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* src/cff/cf2font.c (cf2_computeDarkening): Change overflow
detection to use logarithms and clamp `scaledStem'.
This commit is contained in:
Dave Arnold 2014-10-02 06:32:32 +02:00 committed by Werner Lemberg
parent 74d0aad22c
commit 537c55d39d
2 changed files with 30 additions and 15 deletions
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7
ChangeLog
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@ -1,3 +1,10 @@
2014-10-02 Dave Arnold <darnold@adobe.com>
[cff] Fix Savannah bug #43271.
* src/cff/cf2font.c (cf2_computeDarkening): Change overflow
detection to use logarithms and clamp `scaledStem'.
2014-10-01 Alexei Podtelezhnikov <apodtele@gmail.com>
* src/base/ftcalc.c: Remove miscellaneous type casts.

38
src/cff/cf2font.c
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@ -105,6 +105,7 @@
/* adjusting for emRatio converts darkenAmount to character */
/* space (font units). */
CF2_Fixed stemWidthPer1000, scaledStem;
FT_Int logBase2;
*darkenAmount = 0;
@ -131,25 +132,32 @@
/* convert from true character space to 1000 unit character space; */
/* add synthetic emboldening effect */
/* we have to assure that the computation of `scaledStem' */
/* and `stemWidthPer1000' don't overflow */
/* `stemWidthPer1000' will not overflow for a legitimate font */
stemWidthPer1000 = FT_MulFix( stemWidth + boldenAmount, emRatio );
if ( emRatio > CF2_FIXED_ONE &&
stemWidthPer1000 <= ( stemWidth + boldenAmount ) )
{
stemWidthPer1000 = 0; /* to pacify compiler */
scaledStem = cf2_intToFixed( x4 );
}
else
{
scaledStem = FT_MulFix( stemWidthPer1000, ppem );
/* `scaledStem' can easily overflow, so we must clamp its maximum */
/* value; the test doesn't need to be precise, but must be */
/* conservative. The clamp value (default 2333) where */
/* `darkenAmount' is zero is well below the overflow value of */
/* 32767. */
/* */
/* FT_MSB computes the integer part of the base 2 logarithm. The */
/* number of bits for the product is 1 or 2 more than the sum of */
/* logarithms; remembering that the 16 lowest bits of the fraction */
/* are dropped this is correct to within a factor of almost 4. */
/* For example, 0x80.0000 * 0x80.0000 = 0x4000.0000 is 23+23 and */
/* is flagged as possible overflow because 0xff.ffff * 0xff.ffff = */
/* 0xffff.fe00 is also 23+23. */
if ( ppem > CF2_FIXED_ONE &&
scaledStem <= stemWidthPer1000 )
scaledStem = cf2_intToFixed( x4 );
}
logBase2 = FT_MSB( (FT_UInt32)stemWidthPer1000 ) +
FT_MSB( (FT_UInt32)ppem );
if ( logBase2 >= 46 )
/* possible overflow */
scaledStem = cf2_intToFixed( x4 );
else
scaledStem = FT_MulFix( stemWidthPer1000, ppem );
/* now apply the darkening parameters */