AMD Typewriter x86 사용자 설명서

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):

FLD