User's Manual

Take Advantage of the FSINCOS Instruction 105

22007E/0—November 1999 AMD Athlon™ Processor x86 Code Optimization

Since out-of-range arguments are extremely uncommon, the

conditional branch will be perfectly predicted, and the other

instructions used to guard the trigonometric instruction can

execute in parallel to it.

Take Advantage of the FSINCOS Instruction

Frequently, a piece of code that needs to compute the sine of an

argument also needs to compute the cosine of that same

argument. In such cases, the FSINCOS instruction should be

used to compute both trigonometric functions concurrently,

which is faster than using separate FSIN and FCOS instructions

to accomplish the same task.

Example 1 (Avoid):

FLD QWORD PTR [x]

FLD DWORD PTR [two_to_the_63]

FCOMIP ST,ST(1)

JBE $in_range

CALL $reduce_range

$in_range:

FLD ST(0)

FCOS

FSTP QWORD PTR [cosine_x]

FSIN

FSTP QWORD PTR [sine_x]

Example 2 (Preferred):