Connect SHL/SHR operations to the Arithmetic table (#1166)

* Add corresponding arithmetic operations to shift ones

* Include SHL/SHR in the arithmetic CTL

* Prevent overflow

* Expand documentation for ctl_data_ternops()

evm/src/all_stark.rs

@@ -108,7 +108,10 @@ pub(crate) fn all_cross_table_lookups<F: Field>() -> Vec<CrossTableLookup<F>> {
 
 fn ctl_arithmetic<F: Field>() -> CrossTableLookup<F> {
     CrossTableLookup::new(
-        vec![cpu_stark::ctl_arithmetic_rows()],
+        vec![
+            cpu_stark::ctl_arithmetic_base_rows(),
+            cpu_stark::ctl_arithmetic_shift_rows(),
+        ],
         arithmetic_stark::ctl_arithmetic_rows(),
     )
 }

evm/src/cpu/cpu_stark.rs

@@ -59,12 +59,23 @@ fn ctl_data_binops<F: Field>(ops: &[usize]) -> Vec<Column<F>> {
 }
 
 /// Create the vector of Columns corresponding to the three inputs and
-/// one output of a ternary operation.
-fn ctl_data_ternops<F: Field>(ops: &[usize]) -> Vec<Column<F>> {
+/// one output of a ternary operation. By default, ternary operations use
+/// the first three memory channels, and the last one for the result (binary
+/// operations do not use the third inputs).
+///
+/// Shift operations are different, as they are simulated with `MUL` or `DIV`
+/// on the arithmetic side. We first convert the shift into the multiplicand
+/// (in case of `SHL`) or the divisor (in case of `SHR`), making the first memory
+/// channel not directly usable. We overcome this by adding an offset of 1 in
+/// case of shift operations, which will skip the first memory channel and use the
+/// next three as ternary inputs. Because both `MUL` and `DIV` are binary operations,
+/// the last memory channel used for the inputs will be safely ignored.
+fn ctl_data_ternops<F: Field>(ops: &[usize], is_shift: bool) -> Vec<Column<F>> {
+    let offset = is_shift as usize;
     let mut res = Column::singles(ops).collect_vec();
-    res.extend(Column::singles(COL_MAP.mem_channels[0].value));
-    res.extend(Column::singles(COL_MAP.mem_channels[1].value));
-    res.extend(Column::singles(COL_MAP.mem_channels[2].value));
+    res.extend(Column::singles(COL_MAP.mem_channels[offset].value));
+    res.extend(Column::singles(COL_MAP.mem_channels[offset + 1].value));
+    res.extend(Column::singles(COL_MAP.mem_channels[offset + 2].value));
     res.extend(Column::singles(
         COL_MAP.mem_channels[NUM_GP_CHANNELS - 1].value,
     ));
@@ -79,7 +90,7 @@ pub fn ctl_filter_logic<F: Field>() -> Column<F> {
     Column::sum([COL_MAP.op.and, COL_MAP.op.or, COL_MAP.op.xor])
 }
 
-pub fn ctl_arithmetic_rows<F: Field>() -> TableWithColumns<F> {
+pub fn ctl_arithmetic_base_rows<F: Field>() -> TableWithColumns<F> {
     const OPS: [usize; 14] = [
         COL_MAP.op.add,
         COL_MAP.op.sub,
@@ -101,7 +112,42 @@ pub fn ctl_arithmetic_rows<F: Field>() -> TableWithColumns<F> {
     // (also `ops` is used as the operation filter). The list of
     // operations includes binary operations which will simply ignore
     // the third input.
-    TableWithColumns::new(Table::Cpu, ctl_data_ternops(&OPS), Some(Column::sum(OPS)))
+    TableWithColumns::new(
+        Table::Cpu,
+        ctl_data_ternops(&OPS, false),
+        Some(Column::sum(OPS)),
+    )
+}
+
+pub fn ctl_arithmetic_shift_rows<F: Field>() -> TableWithColumns<F> {
+    const OPS: [usize; 14] = [
+        COL_MAP.op.add,
+        COL_MAP.op.sub,
+        // SHL is interpreted as MUL on the arithmetic side
+        COL_MAP.op.shl,
+        COL_MAP.op.lt,
+        COL_MAP.op.gt,
+        COL_MAP.op.addfp254,
+        COL_MAP.op.mulfp254,
+        COL_MAP.op.subfp254,
+        COL_MAP.op.addmod,
+        COL_MAP.op.mulmod,
+        COL_MAP.op.submod,
+        // SHR is interpreted as DIV on the arithmetic side
+        COL_MAP.op.shr,
+        COL_MAP.op.mod_,
+        COL_MAP.op.byte,
+    ];
+    // Create the CPU Table whose columns are those with the three
+    // inputs and one output of the ternary operations listed in `ops`
+    // (also `ops` is used as the operation filter). The list of
+    // operations includes binary operations which will simply ignore
+    // the third input.
+    TableWithColumns::new(
+        Table::Cpu,
+        ctl_data_ternops(&OPS, true),
+        Some(Column::sum([COL_MAP.op.shl, COL_MAP.op.shr])),
+    )
 }
 
 pub const MEM_CODE_CHANNEL_IDX: usize = 0;

evm/src/cpu/shift.rs

@@ -54,7 +54,7 @@ pub(crate) fn eval_packed<P: PackedField>(
     // (in the case of left shift) or DIV (in the case of right shift)
     // in the arithmetic table. Specifically, the mapping is
     //
-    // 0 -> 0  (value to be shifted is the same)
+    // 1 -> 0  (value to be shifted is the same)
     // 2 -> 1  (two_exp becomes the multiplicand (resp. divisor))
     // last -> last  (output is the same)
 }

evm/src/witness/operation.rs

@@ -3,6 +3,7 @@ use itertools::Itertools;
 use keccak_hash::keccak;
 use plonky2::field::types::Field;
 
+use crate::arithmetic::BinaryOperator;
 use crate::cpu::columns::CpuColumnsView;
 use crate::cpu::kernel::aggregator::KERNEL;
 use crate::cpu::kernel::assembler::BYTES_PER_OFFSET;
@@ -470,6 +471,7 @@ fn append_shift<F: Field>(
     state: &mut GenerationState<F>,
     mut row: CpuColumnsView<F>,
     input0: U256,
+    input1: U256,
     log_in0: MemoryOp,
     log_in1: MemoryOp,
     result: U256,
@@ -489,6 +491,20 @@ fn append_shift<F: Field>(
         channel.addr_virtual = F::from_canonical_usize(lookup_addr.virt);
     }
 
+    // Convert the shift, and log the corresponding arithmetic operation.
+    let input0 = if input0 > U256::from(255u64) {
+        U256::zero()
+    } else {
+        U256::one() << input0
+    };
+    let operator = if row.op.shl.is_one() {
+        BinaryOperator::Mul
+    } else {
+        BinaryOperator::Div
+    };
+    let operation = arithmetic::Operation::binary(operator, input1, input0);
+
+    state.traces.push_arithmetic(operation);
     state.traces.push_memory(log_in0);
     state.traces.push_memory(log_in1);
     state.traces.push_memory(log_out);
@@ -508,7 +524,7 @@ pub(crate) fn generate_shl<F: Field>(
     } else {
         input1 << input0
     };
-    append_shift(state, row, input0, log_in0, log_in1, result)
+    append_shift(state, row, input0, input1, log_in0, log_in1, result)
 }
 
 pub(crate) fn generate_shr<F: Field>(
@@ -523,7 +539,7 @@ pub(crate) fn generate_shr<F: Field>(
     } else {
         input1 >> input0
     };
-    append_shift(state, row, input0, log_in0, log_in1, result)
+    append_shift(state, row, input0, input1, log_in0, log_in1, result)
 }
 
 pub(crate) fn generate_syscall<F: Field>(