rtvm_interpreter/instructions/
arithmetic.rs

1use super::i256::{i256_div, i256_mod};
2use crate::{
3    gas,
4    primitives::{Spec, U256},
5    Host, Interpreter,
6};
7
8pub fn add<H: Host + ?Sized>(interpreter: &mut Interpreter, _host: &mut H) {
9    gas!(interpreter, gas::VERYLOW);
10    pop_top!(interpreter, op1, op2);
11    *op2 = op1.wrapping_add(*op2);
12}
13
14pub fn mul<H: Host + ?Sized>(interpreter: &mut Interpreter, _host: &mut H) {
15    gas!(interpreter, gas::LOW);
16    pop_top!(interpreter, op1, op2);
17    *op2 = op1.wrapping_mul(*op2);
18}
19
20pub fn sub<H: Host + ?Sized>(interpreter: &mut Interpreter, _host: &mut H) {
21    gas!(interpreter, gas::VERYLOW);
22    pop_top!(interpreter, op1, op2);
23    *op2 = op1.wrapping_sub(*op2);
24}
25
26pub fn div<H: Host + ?Sized>(interpreter: &mut Interpreter, _host: &mut H) {
27    gas!(interpreter, gas::LOW);
28    pop_top!(interpreter, op1, op2);
29    if *op2 != U256::ZERO {
30        *op2 = op1.wrapping_div(*op2);
31    }
32}
33
34pub fn sdiv<H: Host + ?Sized>(interpreter: &mut Interpreter, _host: &mut H) {
35    gas!(interpreter, gas::LOW);
36    pop_top!(interpreter, op1, op2);
37    *op2 = i256_div(op1, *op2);
38}
39
40pub fn rem<H: Host + ?Sized>(interpreter: &mut Interpreter, _host: &mut H) {
41    gas!(interpreter, gas::LOW);
42    pop_top!(interpreter, op1, op2);
43    if *op2 != U256::ZERO {
44        *op2 = op1.wrapping_rem(*op2);
45    }
46}
47
48pub fn smod<H: Host + ?Sized>(interpreter: &mut Interpreter, _host: &mut H) {
49    gas!(interpreter, gas::LOW);
50    pop_top!(interpreter, op1, op2);
51    *op2 = i256_mod(op1, *op2)
52}
53
54pub fn addmod<H: Host + ?Sized>(interpreter: &mut Interpreter, _host: &mut H) {
55    gas!(interpreter, gas::MID);
56    pop_top!(interpreter, op1, op2, op3);
57    *op3 = op1.add_mod(op2, *op3)
58}
59
60pub fn mulmod<H: Host + ?Sized>(interpreter: &mut Interpreter, _host: &mut H) {
61    gas!(interpreter, gas::MID);
62    pop_top!(interpreter, op1, op2, op3);
63    *op3 = op1.mul_mod(op2, *op3)
64}
65
66pub fn exp<H: Host + ?Sized, SPEC: Spec>(interpreter: &mut Interpreter, _host: &mut H) {
67    pop_top!(interpreter, op1, op2);
68    gas_or_fail!(interpreter, gas::exp_cost(SPEC::SPEC_ID, *op2));
69    *op2 = op1.pow(*op2);
70}
71
72/// In the yellow paper `SIGNEXTEND` is defined to take two inputs, we will call them
73/// `x` and `y`, and produce one output. The first `t` bits of the output (numbering from the
74/// left, starting from 0) are equal to the `t`-th bit of `y`, where `t` is equal to
75/// `256 - 8(x + 1)`. The remaining bits of the output are equal to the corresponding bits of `y`.
76/// Note: if `x >= 32` then the output is equal to `y` since `t <= 0`. To efficiently implement
77/// this algorithm in the case `x < 32` we do the following. Let `b` be equal to the `t`-th bit
78/// of `y` and let `s = 255 - t = 8x + 7` (this is effectively the same index as `t`, but
79/// numbering the bits from the right instead of the left). We can create a bit mask which is all
80/// zeros up to and including the `t`-th bit, and all ones afterwards by computing the quantity
81/// `2^s - 1`. We can use this mask to compute the output depending on the value of `b`.
82/// If `b == 1` then the yellow paper says the output should be all ones up to
83/// and including the `t`-th bit, followed by the remaining bits of `y`; this is equal to
84/// `y | !mask` where `|` is the bitwise `OR` and `!` is bitwise negation. Similarly, if
85/// `b == 0` then the yellow paper says the output should start with all zeros, then end with
86/// bits from `b`; this is equal to `y & mask` where `&` is bitwise `AND`.
87pub fn signextend<H: Host + ?Sized>(interpreter: &mut Interpreter, _host: &mut H) {
88    gas!(interpreter, gas::LOW);
89    pop_top!(interpreter, ext, x);
90    // For 31 we also don't need to do anything.
91    if ext < U256::from(31) {
92        let ext = ext.as_limbs()[0];
93        let bit_index = (8 * ext + 7) as usize;
94        let bit = x.bit(bit_index);
95        let mask = (U256::from(1) << bit_index) - U256::from(1);
96        *x = if bit { *x | !mask } else { *x & mask };
97    }
98}
rtvm_interpreter/instructions/arithmetic.rs

rtvm_interpreter/instructions/
arithmetic.rs
