feat: extension field instructions change stack size

Both instructions `xx_add` and `xx_mul` pop both their operands,
shrinking the stack by 3 elements.

triton-vm/src/instruction.rs

@@ -188,12 +188,12 @@ impl<Dest: PartialEq + Default> AnInstruction<Dest> {
             Pow => 30,
             DivMod => 20,
             PopCount => 28,
-            XxAdd => 80,
-            XxMul => 88,
-            XInvert => 96,
-            XbMul => 66,
-            ReadIo => 104,
-            WriteIo => 74,
+            XxAdd => 66,
+            XxMul => 74,
+            XInvert => 80,
+            XbMul => 82,
+            ReadIo => 88,
+            WriteIo => 90,
         }
     }
 
@@ -355,8 +355,8 @@ impl<Dest: PartialEq + Default> AnInstruction<Dest> {
             Pow => -1,
             DivMod => 0,
             PopCount => 0,
-            XxAdd => 0,
-            XxMul => 0,
+            XxAdd => -3,
+            XxMul => -3,
             XInvert => 0,
             XbMul => -1,
             ReadIo => 1,

triton-vm/src/op_stack.rs

@@ -113,11 +113,6 @@ impl OpStack {
         self.stack[top_of_stack_index - stack_element_index]
     }
 
-    pub(crate) fn peek_at_top_extension_field_element(&self) -> XFieldElement {
-        let coefficients = [self.peek_at(ST0), self.peek_at(ST1), self.peek_at(ST2)];
-        XFieldElement::new(coefficients)
-    }
-
     pub(crate) fn swap_top_with(&mut self, stack_element: OpStackElement) {
         let stack_element_index = usize::from(stack_element);
         let top_of_stack_index = self.stack.len() - 1;

triton-vm/src/table/processor_table.rs

@@ -2058,23 +2058,18 @@ impl ExtProcessorTable {
             circuit_builder.input(NextBaseRow(col.master_base_table_index()))
         };
 
-        let st0_becomes_st0_plus_st3 =
-            next_base_row(ST0) - (curr_base_row(ST0) + curr_base_row(ST3));
-        let st1_becomes_st1_plus_st4 =
-            next_base_row(ST1) - (curr_base_row(ST1) + curr_base_row(ST4));
-        let st2_becomes_st2_plus_st5 =
-            next_base_row(ST2) - (curr_base_row(ST2) + curr_base_row(ST5));
-
+        let st0_becomes_st0_plus_st3 = next_base_row(ST0) - curr_base_row(ST0) - curr_base_row(ST3);
+        let st1_becomes_st1_plus_st4 = next_base_row(ST1) - curr_base_row(ST1) - curr_base_row(ST4);
+        let st2_becomes_st2_plus_st5 = next_base_row(ST2) - curr_base_row(ST2) - curr_base_row(ST5);
         let specific_constraints = vec![
             st0_becomes_st0_plus_st3,
             st1_becomes_st1_plus_st4,
             st2_becomes_st2_plus_st5,
         ];
+
         [
             specific_constraints,
-            Self::instruction_group_op_stack_remains_and_top_three_elements_unconstrained(
-                circuit_builder,
-            ),
+            Self::constraints_for_shrinking_stack_by_3_and_top_3_unconstrained(circuit_builder),
             Self::instruction_group_step_1(circuit_builder),
             Self::instruction_group_keep_ram(circuit_builder),
         ]
@@ -2113,9 +2108,7 @@ impl ExtProcessorTable {
         ];
         [
             specific_constraints,
-            Self::instruction_group_op_stack_remains_and_top_three_elements_unconstrained(
-                circuit_builder,
-            ),
+            Self::constraints_for_shrinking_stack_by_3_and_top_3_unconstrained(circuit_builder),
             Self::instruction_group_step_1(circuit_builder),
             Self::instruction_group_keep_ram(circuit_builder),
         ]
@@ -2378,6 +2371,33 @@ impl ExtProcessorTable {
             + write_io_deselector * running_evaluation_updates
     }
 
+    fn constraints_for_shrinking_stack_by_3_and_top_3_unconstrained(
+        circuit_builder: &ConstraintCircuitBuilder<DualRowIndicator>,
+    ) -> Vec<ConstraintCircuitMonad<DualRowIndicator>> {
+        let constant = |c: u64| circuit_builder.b_constant(c.into());
+        let curr_base_row = |col: ProcessorBaseTableColumn| {
+            circuit_builder.input(CurrentBaseRow(col.master_base_table_index()))
+        };
+        let next_base_row = |col: ProcessorBaseTableColumn| {
+            circuit_builder.input(NextBaseRow(col.master_base_table_index()))
+        };
+
+        vec![
+            next_base_row(ST3) - curr_base_row(ST6),
+            next_base_row(ST4) - curr_base_row(ST7),
+            next_base_row(ST5) - curr_base_row(ST8),
+            next_base_row(ST6) - curr_base_row(ST9),
+            next_base_row(ST7) - curr_base_row(ST10),
+            next_base_row(ST8) - curr_base_row(ST11),
+            next_base_row(ST9) - curr_base_row(ST12),
+            next_base_row(ST10) - curr_base_row(ST13),
+            next_base_row(ST11) - curr_base_row(ST14),
+            next_base_row(ST12) - curr_base_row(ST15),
+            next_base_row(OpStackPointer) - curr_base_row(OpStackPointer) + constant(3),
+            Self::running_product_op_stack_accounts_for_shrinking_stack_by(circuit_builder, 3),
+        ]
+    }
+
     fn stack_shrinks_by_any_of(
         circuit_builder: &ConstraintCircuitBuilder<DualRowIndicator>,
         shrinkages: &[usize],

triton-vm/src/vm.rs

@@ -664,15 +664,15 @@ impl<'pgm> VMState<'pgm> {
 
     fn xx_add(&mut self) -> Result<Vec<CoProcessorCall>> {
         let lhs = self.op_stack.pop_extension_field_element()?;
-        let rhs = self.op_stack.peek_at_top_extension_field_element();
+        let rhs = self.op_stack.pop_extension_field_element()?;
         self.op_stack.push_extension_field_element(lhs + rhs);
         self.instruction_pointer += 1;
         Ok(vec![])
     }
 
     fn xx_mul(&mut self) -> Result<Vec<CoProcessorCall>> {
         let lhs = self.op_stack.pop_extension_field_element()?;
-        let rhs = self.op_stack.peek_at_top_extension_field_element();
+        let rhs = self.op_stack.pop_extension_field_element()?;
         self.op_stack.push_extension_field_element(lhs * rhs);
         self.instruction_pointer += 1;
         Ok(vec![])