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Instruction Set (Continued)

FPU Instruction Summary Issues

All references to TOS and ST(n) refer to stack layout prior

to execution. Values popped off the stack are discarded.

A pop from the stack increments the top of stack pointer.

A push to the stack decrements the top of stack pointer.

Issues:

For FCOS, FSIN, FSINCOS and FPTAN, time shown

is for absolute value of TOS < 3p/4. Add 90 clock

counts for argument reduction if outside this range.

For FCOS, clock count is 141 if TOS <

π/4 and clock

count is 92 if

π/4 < TOS > π/2.

For FSIN, clock count is 81 to 82 if absolute value of

TOS <

π/4.

For F2XM1, clock count is 92 if absolute value of TOS

<0.5.

For FPATAN, clock count is 97 if ST(1)/TOS <

π/32.

For FYL2XP1, clock count is 170 if TOS is out of range

and regular FYL2X is called.

The following opcodes are reserved:

D9D7, D9E2, D9E7, DDFC, DED8, DEDA, DEDC,

DEDD, DEDE, DFFC.

If a reserved opcode is executed, and unpredictable

results may occur (exceptions are not generated).

FSUBRP Floating Point Subtract Reverse, Pop

DE [1110 0 n]

ST(n) <--- TOS - ST(n); then pop TOS

4 - 9

FISUB Floating Point Integer Subtract

32-bit Integer

DA [mod 100 r/m]

TOS <--- TOS - M.SI

14 - 29

16-bit Integer

DE [mod 100 r/m]

TOS <--- TOS - M.WI

14 - 27

FISUBR Floating Point Integer Subtract Reverse

32-bit Integer Reversed

DA [mod 101 r/m]

TOS <--- M.SI - TOS

14 - 29

16-bit Integer Reversed

DE [mod 101 r/m]

TOS <--- M.WI - TOS

14 - 27

FTST Test Top of Stack

D9 E4

CC set by TOS - 0.0

FUCOM Unordered Compare

DD [1110 0 n]

CC set by TOS - ST(n)

FUCOMP Unordered Compare, Pop

DD [1110 1 n]

CC set by TOS - ST(n); then pop TOS

FUCOMPP Unordered Compare, Pop two

elements

DA E9

CC set by TOS - ST(I); then pop TOS and ST(1)

FWAIT Wait

Wait for FPU not busy

FXAM Report Class of Operand

D9 E5

CC <--- Class of TOS

FXCH Exchange Register with TOS

D9 [1100 1 n]

TOS <--> ST(n) Exchange

FXTRACT Extract Exponent

D9 F4

temp <--- TOS;

TOS <--- exponent (temp); then

push significant (temp) onto stack

11 - 16

FLY2X Function Eval. y

× Log2(x)

D9 F1

ST(1) <--- ST(1)

× Log

2(TOS); then pop TOS

145 - 154

FLY2XP1 Function Eval. y

× Log2(x+1)

D9 F9

ST(1) <--- ST(1)

× Log

2(1+TOS); then pop TOS

131 - 133

Table 8-29. FPU Instruction Set Summary (Continued)

FPU Instruction

Opcode

Operation

Clock

Count

Issue

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