Commit 15fef219d6ed191ef09efad4d8a3a4f4d2b7158b
2022-06-29T11:48:10
New function `FT_MulAddFix` to compute the sum of fixed-point products. This function, based on the code of `FT_MulFix`, uses 64-bit precision internally for intermediate computations. * include/freetype/internal/ftcalc.h, base/ftcalc.c (FT_MulAddFix): Implement it.
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diff --git a/include/freetype/internal/ftcalc.h b/include/freetype/internal/ftcalc.h
index e6a87db..96a52b5 100644
--- a/include/freetype/internal/ftcalc.h
+++ b/include/freetype/internal/ftcalc.h
@@ -278,6 +278,40 @@ FT_BEGIN_HEADER
FT_Long c );
+ /**************************************************************************
+ *
+ * @function:
+ * FT_MulAddFix
+ *
+ * @description:
+ * Compute `(s[0] * f[0] + s[1] * f[1] + ...) / 0x10000`, where `s[n]` is
+ * usually a 16.16 scalar.
+ *
+ * @input:
+ * s ::
+ * The array of scalars.
+ * f ::
+ * The array of factors.
+ * count ::
+ * The number of entries in the array.
+ *
+ * @return:
+ * The result of `(s[0] * f[0] + s[1] * f[1] + ...) / 0x10000`.
+ *
+ * @note:
+ * This function is currently used for the scaled delta computation of
+ * variation stores. It internally uses 64-bit data types when
+ * available, otherwise it emulates 64-bit math by using 32-bit
+ * operations, which produce a correct result but most likely at a slower
+ * performance in comparison to the implementation base on `int64_t`.
+ *
+ */
+ FT_BASE( FT_Int32 )
+ FT_MulAddFix( FT_Fixed* s,
+ FT_Int32* f,
+ FT_UInt count );
+
+
/*
* A variant of FT_Matrix_Multiply which scales its result afterwards. The
* idea is that both `a' and `b' are scaled by factors of 10 so that the
diff --git a/src/base/ftcalc.c b/src/base/ftcalc.c
index 6c1e7fb..0f1395d 100644
--- a/src/base/ftcalc.c
+++ b/src/base/ftcalc.c
@@ -1085,4 +1085,64 @@
}
+ FT_BASE_DEF( FT_Int32 )
+ FT_MulAddFix( FT_Fixed* s,
+ FT_Int32* f,
+ FT_UInt count )
+ {
+ FT_UInt i;
+ FT_Int64 temp;
+
+
+#ifdef FT_INT64
+
+ for ( i = 0; i < count; ++i )
+ temp += (FT_Int64)s[i] * f[i];
+
+ return temp >> 16;
+
+#else
+
+ temp.hi = 0;
+ temp.lo = 0;
+
+ for ( i = 0; i < count; ++i )
+ {
+ FT_Int64 multResult;
+
+ FT_Int sign = 1;
+ FT_UInt32 carry = 0;
+
+ FT_UInt32 scalar;
+ FT_UInt32 factor;
+
+
+ scalar = (FT_UInt32)s[i];
+ factor = (FT_UInt32)f[i];
+
+ FT_MOVE_SIGN( s[i], scalar, sign );
+ FT_MOVE_SIGN( f[i], factor, sign );
+
+ ft_multo64( scalar, factor, &multResult );
+
+ if ( sign < 0 )
+ {
+ /* Emulated `FT_Int64` negation. */
+ carry = ( multResult.lo == 0 );
+
+ multResult.lo = ~multResult.lo + 1;
+ multResult.hi = ~multResult.hi + carry;
+ }
+
+ FT_Add64( &temp, &multResult, &temp );
+ }
+
+ return (FT_Int32)( ( (FT_Int32)( temp.hi & 0xFFFF ) << 16 ) |
+ ( temp.lo >> 16 ) );
+
+#endif /* !FT_INT64 */
+
+ }
+
+
/* END */