b5ebfadbd6
The start of the bytecode prelude contains 6 numbers telling the amount of stack needed for the Python values and exceptions, and the signature of the function. Prior to this patch these numbers were all encoded one after the other (2x variable unsigned integers, then 4x bytes), but using so many bytes is unnecessary. An entropy analysis of around 150,000 bytecode functions from the CPython standard library showed that the optimal Shannon coding would need about 7.1 bits on average to encode these 6 numbers, compared to the existing 48 bits. This patch attempts to get close to this optimal value by packing the 6 numbers into a single, varible-length unsigned integer via bit-wise interleaving. The interleaving scheme is chosen to minimise the average number of bytes needed, and at the same time keep the scheme simple enough so it can be implemented without too much overhead in code size or speed. The scheme requires about 10.5 bits on average to store the 6 numbers. As a result most functions which originally took 6 bytes to encode these 6 numbers now need only 1 byte (in 80% of cases).
232 lines
10 KiB
C
232 lines
10 KiB
C
/*
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* This file is part of the MicroPython project, http://micropython.org/
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*
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* The MIT License (MIT)
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*
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* Copyright (c) 2013, 2014 Damien P. George
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* Copyright (c) 2014 Paul Sokolovsky
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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* THE SOFTWARE.
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*/
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#ifndef MICROPY_INCLUDED_PY_BC_H
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#define MICROPY_INCLUDED_PY_BC_H
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#include "py/runtime.h"
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#include "py/objfun.h"
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// bytecode layout:
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//
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// func signature : var uint
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// contains six values interleaved bit-wise as: xSSSSEAA [xFSSKAED repeated]
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// x = extension another byte follows
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// S = n_state - 1 number of entries in Python value stack
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// E = n_exc_stack number of entries in exception stack
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// F = scope_flags four bits of flags, MP_SCOPE_FLAG_xxx
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// A = n_pos_args number of arguments this function takes
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// K = n_kwonly_args number of keyword-only arguments this function takes
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// D = n_def_pos_args number of default positional arguments
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//
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// code_info_size : var uint | code_info_size counts bytes in this chunk
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// simple_name : var qstr |
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// source_file : var qstr |
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// <line number info> |
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// <word alignment padding> | only needed if bytecode contains pointers
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//
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// local_num0 : byte |
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// ... : byte |
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// local_numN : byte | N = num_cells
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// 255 : byte | end of list sentinel
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// <bytecode> |
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//
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//
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// constant table layout:
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//
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// argname0 : obj (qstr)
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// ... : obj (qstr)
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// argnameN : obj (qstr) N = num_pos_args + num_kwonly_args
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// const0 : obj
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// constN : obj
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#define MP_BC_PRELUDE_SIG_ENCODE(S, E, scope, out_byte, out_env) \
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do { \
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/*// Get values to store in prelude */ \
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size_t F = scope->scope_flags & 0x0f; /* only need to store lower 4 flag bits */ \
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size_t A = scope->num_pos_args; \
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size_t K = scope->num_kwonly_args; \
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size_t D = scope->num_def_pos_args; \
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\
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/* Adjust S to shrink range, to compress better */ \
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S -= 1; \
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\
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/* Encode prelude */ \
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/* xSSSSEAA */ \
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uint8_t z = (S & 0xf) << 3 | (E & 1) << 2 | (A & 3); \
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S >>= 4; \
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E >>= 1; \
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A >>= 2; \
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while (S | E | F | A | K | D) { \
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out_byte(out_env, 0x80 | z); \
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/* xFSSKAED */ \
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z = (F & 1) << 6 | (S & 3) << 4 | (K & 1) << 3 \
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| (A & 1) << 2 | (E & 1) << 1 | (D & 1); \
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S >>= 2; \
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E >>= 1; \
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F >>= 1; \
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A >>= 1; \
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K >>= 1; \
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D >>= 1; \
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} \
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out_byte(out_env, z); \
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} while (0)
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#define MP_BC_PRELUDE_SIG_DECODE_INTO(ip, S, E, F, A, K, D) \
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do { \
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uint8_t z = *(ip)++; \
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/* xSSSSEAA */ \
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S = (z >> 3) & 0xf; \
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E = (z >> 2) & 0x1; \
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F = 0; \
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A = z & 0x3; \
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K = 0; \
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D = 0; \
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for (unsigned n = 0; z & 0x80; ++n) { \
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z = *(ip)++; \
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/* xFSSKAED */ \
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S |= (z & 0x30) << (2 * n); \
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E |= (z & 0x02) << n; \
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F |= ((z & 0x40) >> 6) << n; \
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A |= (z & 0x4) << n; \
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K |= ((z & 0x08) >> 3) << n; \
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D |= (z & 0x1) << n; \
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} \
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S += 1; \
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} while (0)
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#define MP_BC_PRELUDE_SIG_DECODE(ip) \
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size_t n_state, n_exc_stack, scope_flags, n_pos_args, n_kwonly_args, n_def_pos_args; \
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MP_BC_PRELUDE_SIG_DECODE_INTO(ip, n_state, n_exc_stack, scope_flags, n_pos_args, n_kwonly_args, n_def_pos_args)
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// Sentinel value for mp_code_state_t.exc_sp_idx
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#define MP_CODE_STATE_EXC_SP_IDX_SENTINEL ((uint16_t)-1)
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// To convert mp_code_state_t.exc_sp_idx to/from a pointer to mp_exc_stack_t
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#define MP_CODE_STATE_EXC_SP_IDX_FROM_PTR(exc_stack, exc_sp) ((exc_sp) + 1 - (exc_stack))
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#define MP_CODE_STATE_EXC_SP_IDX_TO_PTR(exc_stack, exc_sp_idx) ((exc_stack) + (exc_sp_idx) - 1)
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typedef struct _mp_bytecode_prelude_t {
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uint n_state;
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uint n_exc_stack;
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uint scope_flags;
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uint n_pos_args;
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uint n_kwonly_args;
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uint n_def_pos_args;
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qstr qstr_block_name;
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qstr qstr_source_file;
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const byte *line_info;
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const byte *locals;
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const byte *opcodes;
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} mp_bytecode_prelude_t;
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// Exception stack entry
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typedef struct _mp_exc_stack_t {
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const byte *handler;
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// bit 0 is currently unused
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// bit 1 is whether the opcode was SETUP_WITH or SETUP_FINALLY
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mp_obj_t *val_sp;
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// Saved exception
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mp_obj_base_t *prev_exc;
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} mp_exc_stack_t;
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typedef struct _mp_code_state_t {
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// The fun_bc entry points to the underlying function object that is being executed.
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// It is needed to access the start of bytecode and the const_table.
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// It is also needed to prevent the GC from reclaiming the bytecode during execution,
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// because the ip pointer below will always point to the interior of the bytecode.
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mp_obj_fun_bc_t *fun_bc;
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const byte *ip;
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mp_obj_t *sp;
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uint16_t n_state;
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uint16_t exc_sp_idx;
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mp_obj_dict_t *old_globals;
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#if MICROPY_STACKLESS
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struct _mp_code_state_t *prev;
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#endif
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#if MICROPY_PY_SYS_SETTRACE
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struct _mp_code_state_t *prev_state;
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struct _mp_obj_frame_t *frame;
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#endif
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// Variable-length
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mp_obj_t state[0];
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// Variable-length, never accessed by name, only as (void*)(state + n_state)
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//mp_exc_stack_t exc_state[0];
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} mp_code_state_t;
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mp_uint_t mp_decode_uint(const byte **ptr);
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mp_uint_t mp_decode_uint_value(const byte *ptr);
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const byte *mp_decode_uint_skip(const byte *ptr);
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mp_vm_return_kind_t mp_execute_bytecode(mp_code_state_t *code_state, volatile mp_obj_t inject_exc);
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mp_code_state_t *mp_obj_fun_bc_prepare_codestate(mp_obj_t func, size_t n_args, size_t n_kw, const mp_obj_t *args);
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void mp_setup_code_state(mp_code_state_t *code_state, size_t n_args, size_t n_kw, const mp_obj_t *args);
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void mp_bytecode_print(const void *descr, const byte *code, mp_uint_t len, const mp_uint_t *const_table);
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void mp_bytecode_print2(const byte *code, size_t len, const mp_uint_t *const_table);
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const byte *mp_bytecode_print_str(const byte *ip);
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#define mp_bytecode_print_inst(code, const_table) mp_bytecode_print2(code, 1, const_table)
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// Helper macros to access pointer with least significant bits holding flags
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#define MP_TAGPTR_PTR(x) ((void*)((uintptr_t)(x) & ~((uintptr_t)3)))
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#define MP_TAGPTR_TAG0(x) ((uintptr_t)(x) & 1)
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#define MP_TAGPTR_TAG1(x) ((uintptr_t)(x) & 2)
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#define MP_TAGPTR_MAKE(ptr, tag) ((void*)((uintptr_t)(ptr) | (tag)))
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#if MICROPY_PERSISTENT_CODE_LOAD || MICROPY_PERSISTENT_CODE_SAVE
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uint mp_opcode_format(const byte *ip, size_t *opcode_size, bool count_var_uint);
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#endif
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static inline size_t mp_bytecode_get_source_line(const byte *line_info, size_t bc_offset) {
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size_t source_line = 1;
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size_t c;
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while ((c = *line_info)) {
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size_t b, l;
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if ((c & 0x80) == 0) {
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// 0b0LLBBBBB encoding
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b = c & 0x1f;
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l = c >> 5;
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line_info += 1;
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} else {
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// 0b1LLLBBBB 0bLLLLLLLL encoding (l's LSB in second byte)
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b = c & 0xf;
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l = ((c << 4) & 0x700) | line_info[1];
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line_info += 2;
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}
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if (bc_offset >= b) {
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bc_offset -= b;
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source_line += l;
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} else {
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// found source line corresponding to bytecode offset
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break;
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}
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}
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return source_line;
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}
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#endif // MICROPY_INCLUDED_PY_BC_H
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