diff options
Diffstat (limited to 'src/cff/cf2font.c')
| -rw-r--r-- | src/cff/cf2font.c | 39 |
1 files changed, 25 insertions, 14 deletions
diff --git a/src/cff/cf2font.c b/src/cff/cf2font.c index 6e99dc2..83fd348 100644 --- a/src/cff/cf2font.c +++ b/src/cff/cf2font.c @@ -36,6 +36,9 @@ /***************************************************************************/ +#include <ft2build.h> +#include FT_INTERNAL_CALC_H + #include "cf2ft.h" #include "cf2glue.h" @@ -105,6 +108,7 @@ /* adjusting for emRatio converts darkenAmount to character */ /* space (font units). */ CF2_Fixed stemWidthPer1000, scaledStem; + FT_Int logBase2; *darkenAmount = 0; @@ -131,26 +135,33 @@ /* 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 ); - } + /* `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. */ + + 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 ); - if ( ppem > CF2_FIXED_ONE && - scaledStem <= stemWidthPer1000 ) - scaledStem = cf2_intToFixed( x4 ); - } - /* now apply the darkening parameters */ if ( scaledStem < cf2_intToFixed( x1 ) ) |