diff options
| -rw-r--r-- | src/smooth/ftgrays.c | 6 |
1 files changed, 6 insertions, 0 deletions
diff --git a/src/smooth/ftgrays.c b/src/smooth/ftgrays.c index 5ae791872..c550c3303 100644 --- a/src/smooth/ftgrays.c +++ b/src/smooth/ftgrays.c @@ -380,6 +380,12 @@ typedef ptrdiff_t FT_PtrDist; /* each slanted line. Nevertheless, these divisions are noticeable */ /* in the overall performance because flattened curves produce a */ /* very large number of slanted lines. */ + /* */ + /* The division results here are always within ONE_PIXEL. Therefore */ + /* the shift magnitude should be at least PIXEL_BITS wider than the */ + /* divisors to provide sufficient accuracy of the multiply-shift. */ + /* It should not exceed (64 - PIXEL_BITS) to prevent overflowing and */ + /* leave enough room for 64-bit unsigned multiplication however. */ #define FT_UDIVPREP( c, b ) \ FT_Int64 b ## _r = c ? (FT_Int64)( ~(FT_UInt64)0 >> PIXEL_BITS ) / ( b ) \ : 0 |