The description of evmc_storage_status enum design and its relation to the specification in EIP-2200 and others.

Specification

‍This is the EIP-2200 specification with modifications:

the clause tree has been converted to ordered lists to be referenceable,

the cost constant names has been replaced with matching Yellow Paper names.

If gasleft is less than or equal to gas stipend, fail the current call frame with 'out of gas' exception.
If current value equals new value (this is a no-op), G_warmaccess is deducted.
If current value does not equal new value
1. If original value equals current value (this storage slot has not been changed by the current execution context)
  1. If original value is 0, G_sset is deducted.
  2. Otherwise, G_sreset gas is deducted.
    1. If new value is 0, add R_sclear gas to refund counter.
2. If original value does not equal current value (this storage slot is dirty), G_warmaccess gas is deducted. Apply both of the following clauses.
  1. If original value is not 0
    1. If current value is 0 (also means that new value is not 0), remove R_sclear gas from refund counter.
    2. If new value is 0 (also means that current value is not 0), add R_sclear gas to refund counter.
  2. If original value equals new value (this storage slot is reset)
    1. If original value is 0, add G_sset - G_warmaccess to refund counter.
    2. Otherwise, add G_sreset - G_warmaccess gas to refund counter.

Cost constants

Yellow Paper	EIP-2200	EIP-2200 Value	EIP-2929 Value
G_warmaccess	`SLOAD_GAS`	800	100
G_sset	`SSTORE_SET_GAS`	20000	20000
G_sreset	`SSTORE_RESET_GAS`	5000	2900
R_sclear	`SSTORE_CLEARS_SCHEDULE`	15000	15000

Storage change statuses

0 - zero value
X - non-zero value
Y - non-zero value different from X
Z - non-zero value different form X and Y
o - original value
c - current value
v - new value

name	o	c	v	dirty	restored	clause	gas cost	gas refund
ASSIGNED	0	0	0	no	yes	2	G_warmaccess	0
	X	0	0	yes	no	2
	0	Y	Y	yes	no	2
	X	Y	Y	yes	no	2
	Y	Y	Y	no	yes	2
	0	Y	Z	yes	no	3.2
	X	Y	Z	yes	no	3.2
ADDED	0	0	Z	no	no	3.1.1	G_sset	0
DELETED	X	X	0	no	no	3.1.2.1	G_sreset	R_sclear
MODIFIED	X	X	Z	no	no	3.1.2	G_sreset	0
DELETED_ADDED	X	0	Z	yes	no	3.2.1.1	G_warmaccess	-R_sclear
MODIFIED_DELETED	X	Y	0	yes	no	3.2.1.2	G_warmaccess	R_sclear
DELETED_RESTORED	X	0	X	yes	yes	3.2.1.1 + 3.2.2.2	G_warmaccess	-R_sclear + G_sreset - G_warmaccess
ADDED_DELETED	0	Y	0	yes	yes	3.2.2.1	G_warmaccess	G_sset - G_warmaccess
MODIFIED_RESTORED	X	Y	X	yes	yes	3.2.2.2	G_warmaccess	G_sreset - G_warmaccess

Efficient implementation

All distinctive storage change statuses can be unambiguously selected by combination of the 4 following checks:

o ≠ c, i.e. original != current (dirty),
o = v, i.e original == new (restored),
c ≠ 0, i.e current != 0,
v ≠ 0, i.e new != 0.

name	o	c	v	o ≠ c	o = v	c ≠ 0	v ≠ 0	checksum	proof
ASSIGNED	0	0	0	0	1	0	0	4 (0b0100)
	X	0	0	1	0	0	0	8 (0b1000)
	0	Y	Y	1	0	1	1	11 (0b1011)
	X	Y	Y	1	0	1	1	11 (0b1011)
	Y	Y	Y	0	1	1	1	7 (0b0111)
	0	Y	Z	1	0	1	1	11 (0b1011)
	X	Y	Z	1	0	1	1	11 (0b1011)
ADDED	0	0	Z	0	0	0	1	1 (0b0001)
DELETED	X	X	0	0	0	1	0	2 (0b0010)
MODIFIED	X	X	Z	0	0	1	1	3 (0b0011)
DELETED_ADDED	X	0	Z	1	0	0	1	9 (0b1001)
MODIFIED_DELETED	X	Y	0	1	0	1	0	10 (0b1010)
DELETED_RESTORED	X	0	X	1	1	0	1	13 (0b1101)
ADDED_DELETED	0	Y	0	1	1	1	0	14 (0b1110)
MODIFIED_RESTORED	X	Y	X	1	1	1	1	15 (0b1111)
impossible				0	0	0	0	0 (0b0000)	o=c ∧ o≠v ∧ c=0 ⇒ v≠0
				0	1	0	1	5 (0b0101)	o=c ∧ o=v ∧ c=0 ⇒ v=0
				0	1	1	0	6 (0b0110)	o=c ∧ o=v ∧ c≠0 ⇒ v≠0
				1	1	0	0	12 (0b1100)	o≠c ∧ o=v ∧ c=0 ⇒ v≠0