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174 lines
9.6 KiB
174 lines
9.6 KiB
/*
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* Copyright 2018, The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#ifndef ANDROID_APF_APF_H
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#define ANDROID_APF_APF_H
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// A brief overview of APF:
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//
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// APF machine is composed of:
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// 1. A read-only program consisting of bytecodes as described below.
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// 2. Two 32-bit registers, called R0 and R1.
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// 3. Sixteen 32-bit temporary memory slots (cleared between packets).
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// 4. A read-only packet.
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// The program is executed by the interpreter below and parses the packet
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// to determine if the application processor (AP) should be woken up to
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// handle the packet or if can be dropped.
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//
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// APF bytecode description:
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//
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// The APF interpreter uses big-endian byte order for loads from the packet
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// and for storing immediates in instructions.
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//
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// Each instruction starts with a byte composed of:
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// Top 5 bits form "opcode" field, see *_OPCODE defines below.
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// Next 2 bits form "size field", which indicate the length of an immediate
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// value which follows the first byte. Values in this field:
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// 0 => immediate value is 0 and no bytes follow.
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// 1 => immediate value is 1 byte big.
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// 2 => immediate value is 2 bytes big.
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// 3 => immediate value is 4 bytes big.
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// Bottom bit forms "register" field, which indicates which register this
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// instruction operates on.
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//
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// There are three main categories of instructions:
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// Load instructions
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// These instructions load byte(s) of the packet into a register.
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// They load either 1, 2 or 4 bytes, as determined by the "opcode" field.
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// They load into the register specified by the "register" field.
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// The immediate value that follows the first byte of the instruction is
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// the byte offset from the beginning of the packet to load from.
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// There are "indexing" loads which add the value in R1 to the byte offset
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// to load from. The "opcode" field determines which loads are "indexing".
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// Arithmetic instructions
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// These instructions perform simple operations, like addition, on register
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// values. The result of these instructions is always written into R0. One
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// argument of the arithmetic operation is R0's value. The other argument
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// of the arithmetic operation is determined by the "register" field:
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// If the "register" field is 0 then the immediate value following
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// the first byte of the instruction is used as the other argument
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// to the arithmetic operation.
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// If the "register" field is 1 then R1's value is used as the other
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// argument to the arithmetic operation.
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// Conditional jump instructions
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// These instructions compare register R0's value with another value, and if
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// the comparison succeeds, jump (i.e. adjust the program counter). The
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// immediate value that follows the first byte of the instruction
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// represents the jump target offset, i.e. the value added to the program
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// counter if the comparison succeeds. The other value compared is
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// determined by the "register" field:
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// If the "register" field is 0 then another immediate value
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// follows the jump target offset. This immediate value is of the
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// same size as the jump target offset, and represents the value
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// to compare against.
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// If the "register" field is 1 then register R1's value is
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// compared against.
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// The type of comparison (e.g. equal to, greater than etc) is determined
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// by the "opcode" field. The comparison interprets both values being
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// compared as unsigned values.
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//
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// Miscellaneous details:
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//
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// Pre-filled temporary memory slot values
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// When the APF program begins execution, three of the sixteen memory slots
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// are pre-filled by the interpreter with values that may be useful for
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// programs:
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// Slot #11 contains the size (in bytes) of the APF program.
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// Slot #12 contains the total size of the APF buffer (program + data).
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// Slot #13 is filled with the IPv4 header length. This value is calculated
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// by loading the first byte of the IPv4 header and taking the
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// bottom 4 bits and multiplying their value by 4. This value is
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// set to zero if the first 4 bits after the link layer header are
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// not 4, indicating not IPv4.
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// Slot #14 is filled with size of the packet in bytes, including the
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// link-layer header if any.
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// Slot #15 is filled with the filter age in seconds. This is the number of
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// seconds since the AP sent the program to the chipset. This may
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// be used by filters that should have a particular lifetime. For
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// example, it can be used to rate-limit particular packets to one
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// every N seconds.
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// Special jump targets:
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// When an APF program executes a jump to the byte immediately after the last
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// byte of the progam (i.e., one byte past the end of the program), this
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// signals the program has completed and determined the packet should be
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// passed to the AP.
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// When an APF program executes a jump two bytes past the end of the program,
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// this signals the program has completed and determined the packet should
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// be dropped.
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// Jump if byte sequence doesn't match:
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// This is a special instruction to facilitate matching long sequences of
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// bytes in the packet. Initially it is encoded like a conditional jump
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// instruction with two exceptions:
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// The first byte of the instruction is always followed by two immediate
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// fields: The first immediate field is the jump target offset like other
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// conditional jump instructions. The second immediate field specifies the
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// number of bytes to compare.
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// These two immediate fields are followed by a sequence of bytes. These
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// bytes are compared with the bytes in the packet starting from the
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// position specified by the value of the register specified by the
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// "register" field of the instruction.
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// Number of temporary memory slots, see ldm/stm instructions.
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#define MEMORY_ITEMS 16
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// Upon program execution, some temporary memory slots are prefilled:
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#define MEMORY_OFFSET_PROGRAM_SIZE 11 // Size of program (in bytes)
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#define MEMORY_OFFSET_DATA_SIZE 12 // Total size of program + data
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#define MEMORY_OFFSET_IPV4_HEADER_SIZE 13 // 4*([APF_FRAME_HEADER_SIZE]&15)
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#define MEMORY_OFFSET_PACKET_SIZE 14 // Size of packet in bytes.
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#define MEMORY_OFFSET_FILTER_AGE 15 // Age since filter installed in seconds.
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// Leave 0 opcode unused as it's a good indicator of accidental incorrect execution (e.g. data).
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#define LDB_OPCODE 1 // Load 1 byte from immediate offset, e.g. "ldb R0, [5]"
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#define LDH_OPCODE 2 // Load 2 bytes from immediate offset, e.g. "ldh R0, [5]"
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#define LDW_OPCODE 3 // Load 4 bytes from immediate offset, e.g. "ldw R0, [5]"
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#define LDBX_OPCODE 4 // Load 1 byte from immediate offset plus register, e.g. "ldbx R0, [5+R0]"
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#define LDHX_OPCODE 5 // Load 2 byte from immediate offset plus register, e.g. "ldhx R0, [5+R0]"
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#define LDWX_OPCODE 6 // Load 4 byte from immediate offset plus register, e.g. "ldwx R0, [5+R0]"
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#define ADD_OPCODE 7 // Add, e.g. "add R0,5"
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#define MUL_OPCODE 8 // Multiply, e.g. "mul R0,5"
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#define DIV_OPCODE 9 // Divide, e.g. "div R0,5"
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#define AND_OPCODE 10 // And, e.g. "and R0,5"
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#define OR_OPCODE 11 // Or, e.g. "or R0,5"
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#define SH_OPCODE 12 // Left shift, e.g, "sh R0, 5" or "sh R0, -5" (shifts right)
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#define LI_OPCODE 13 // Load signed immediate, e.g. "li R0,5"
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#define JMP_OPCODE 14 // Unconditional jump, e.g. "jmp label"
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#define JEQ_OPCODE 15 // Compare equal and branch, e.g. "jeq R0,5,label"
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#define JNE_OPCODE 16 // Compare not equal and branch, e.g. "jne R0,5,label"
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#define JGT_OPCODE 17 // Compare greater than and branch, e.g. "jgt R0,5,label"
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#define JLT_OPCODE 18 // Compare less than and branch, e.g. "jlt R0,5,label"
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#define JSET_OPCODE 19 // Compare any bits set and branch, e.g. "jset R0,5,label"
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#define JNEBS_OPCODE 20 // Compare not equal byte sequence, e.g. "jnebs R0,5,label,0x1122334455"
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#define EXT_OPCODE 21 // Immediate value is one of *_EXT_OPCODE
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#define LDDW_OPCODE 22 // Load 4 bytes from data address (register + simm): "lddw R0, [5+R1]"
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#define STDW_OPCODE 23 // Store 4 bytes to data address (register + simm): "stdw R0, [5+R1]"
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// Extended opcodes. These all have an opcode of EXT_OPCODE
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// and specify the actual opcode in the immediate field.
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#define LDM_EXT_OPCODE 0 // Load from temporary memory, e.g. "ldm R0,5"
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// Values 0-15 represent loading the different temporary memory slots.
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#define STM_EXT_OPCODE 16 // Store to temporary memory, e.g. "stm R0,5"
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// Values 16-31 represent storing to the different temporary memory slots.
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#define NOT_EXT_OPCODE 32 // Not, e.g. "not R0"
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#define NEG_EXT_OPCODE 33 // Negate, e.g. "neg R0"
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#define SWAP_EXT_OPCODE 34 // Swap, e.g. "swap R0,R1"
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#define MOV_EXT_OPCODE 35 // Move, e.g. "move R0,R1"
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#define EXTRACT_OPCODE(i) (((i) >> 3) & 31)
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#define EXTRACT_REGISTER(i) ((i) & 1)
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#define EXTRACT_IMM_LENGTH(i) (((i) >> 1) & 3)
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#endif // ANDROID_APF_APF_H
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