Intel® Architecture Instruction Set Extensions Programming Reference

A.5 ESCAPE OPCODE INSTRUCTIONS
OPCODE MAP
Opcode maps for coprocessor escape instruction opcodes (x87 floating-point instruction opcodes) are in Table A-7
through Table A-22. These maps are grouped by the first byte of the opcode, from D8-DF. Each of these opcodes
has a ModR/M byte. If the ModR/M byte is within the range of 00H-BFH, bits 3-5 of the ModR/M byte are used as
an opcode extension, similar to the technique used for 1-and 2-byte opcodes (see A.4). If the ModR/M byte is
outside the range of 00H through BFH, the entire ModR/M byte is used as an opcode extension.
A.5.1 Opcode Look-up Examples for Escape Instruction Opcodes
Examples are provided below.
Example A-6. Opcode with ModR/M Byte in the 00H through BFH Range
DD0504000000H can be interpreted as follows:
• The instruction encoded with this opcode can be located in Section . Since the ModR/M byte (05H) is within the
00H through BFH range, bits 3 through 5 (000) of this byte indicate the opcode for an FLD double-real
instruction (see Table A-9).
• The double-real value to be loaded is at 00000004H (the 32-bit displacement that follows and belongs to this
opcode).
Example A-7. Opcode with ModR/M Byte outside the 00H through BFH Range
D8C1H can be interpreted as follows:
• This example illustrates an opcode with a ModR/M byte outside the range of 00H through BFH. The instruction
can be located in Section A.4.
• In Table A-8, the ModR/M byte C1H indicates row C, column 1 (the FADD instruction using ST(0), ST(1) as
operands).
A.5.2 Escape Opcode Instruction Tables
Tables are listed below.
A.5.2.1 Escape Opcodes with D8 as First Byte
Table A-7 and A-8 contain maps for the escape instruction opcodes that begin with D8H. Table A-7 shows the map if the ModR/M
byte is in the range of 00H-BFH. Here, the value of bits 3-5 (the nnn field in Figure A-1) selects the instruction.
Table A-7. D8 Opcode Map When ModR/M Byte is Within 00H to BFH *
nnn Field of ModR/M Byte (refer to Figure A.4)
000B 001B 010B 011B 100B 101B 110B 111B
FADD
FMUL
FCOM FCOMP FSUB
FSUBR
FDIV
FDIVR
single-real
NOTES:
single-real single-real single-real single-real single-real single-real single-real
* All blanks in all opcode maps are reserved and must not be used. Do not depend on the operation of undefined or reserved locations.
Ref. # 319433-014 A-21