mstore(0x40, 0x80)
callvalue
dup1
iszero
tag_1
jumpi
0x00
dup1
revert
tag_1:
pop
0x01
0x00
dup2
swap1
sstore
pop
dataSize(sub_0)
dup1
dataOffset(sub_0)
0x00
codecopy
0x00
return
stop
6080604052348015600f57600080fd5b5060016000819055506085806100266000396000f3fe6080604052348015600f57600080fd
5b506004361060285760003560e01c80630dbe671f14602d575b600080fd5b60336049565b60405180828152602001915050604051
80910390f35b6000548156fea264697066735822122080c75569e2d78735d5756b5cb9adc62ac340594b65f890183145d14a1260fd
a564736f6c63430006070033
6001600081905550 - variable assignment
60 01 60 00 81 90 55 50
EVM executes each instruction top down.
tag2:
// 60 01
0x1
// 60 00
0x0
// 81
dup2
// 90
swap1
// 55
sstore
// 50
pop
0x1 is shorthand for push(0x1) - push the number 1 onto the stack.
EVM - stack machine. Instructions may use values on the stack as arguments, and push results onto the stack. stack - [1 2] after add: stack - [3 2 1]
Store: store before: {} store after: { 0x0 => 0x1} (after pushing 0x1 in 0x0, a simple mapping)
Simulating bytecode - 6001600081905550
60 01: push 1 onto stack
0x1
stack - [0x1]
60 00: push 0 onto stack
0x0
stack - [0x0 0x1]
81 - duplicate second item
dup2
stack - [0x1 0x0 0x1]
90 - swap top two elements
swap1
stack - [0x0 0x1 0x1]
55 - store 0x1 at pos 0x1, uses top two items
sstore
stack - [0x1]
store: { 0x0 => 0x1 }
50: pop stack
stack: []
store { 0x0 => 0x1 }
Resulting state: empty stackm, one item pushed to storage
...
...
pop
0x1
0x0
0x00
dup2
swap1
sstore
pop
0x02
0x01
dup2
swap1
sstore
pop
which translates to sstore(0x0, 0x1) // a = 1; sstore(0x1, 0x2) // b = 2; a stored in 0x0 and b stored in 0x1
packing - each slot can store a max of 32 bytes. We can also pack smaller data blobs into one slot (e.g: two uint128 numbers).
0x1
0x00
dup1
0x0100
exp
dup2
0xffff...
mul
not
and
swap1
dup4
0xffff...
and
mul
or
swap1
sstore
pop
// b = 2
0x2
0x00
0x10
0x0100
exp
dup2
sload
dup2
0xffff...
mul
not
and
swap
dup4
0xffff...
and
mul
or
swap1
sstore
pop
[ b (16 bytes/128 bits) ][ a (16 bytes/128 bits) ] ^ at the position - 0x0