Solution builder for https://www.curta.wtf/golf/2

factorial.go

// The factorial binary builds solutions for the 2nd Curta gas-golfing course.
package main

import (
	"fmt"
	"math/bits"

	"github.com/ethereum/go-ethereum/common"

	. "github.com/solidifylabs/specops" //lint:ignore ST1001 SpecOps DSL is designed to be dot-imported
	"github.com/solidifylabs/specops/specopscli"
	"github.com/solidifylabs/specops/stack"
	"github.com/solidifylabs/specops/types"
)

func code() Code {
	// ----------------------------------------
	// ========== START EDITING HERE ==========
	// vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv

	// Cloned from https://github.com/solidifylabs/specops/tree/main/getting-started

	const (
		_ = Inverted(DUP1) + iota // Result
		Input
	)

	factorial := Code{
		PUSH(1), // Result
		// The selector is irrelevant so just load the input word.
		Fn(CALLDATALOAD, PUSH(4)),

		Fn(JUMPI,
			PUSH("revert"),
			Fn(GT, Input, PUSH(57)),
		),
		stack.ExpectDepth(2),

		Fn(JUMP,
			Fn(SUB,
				PUSH("return"),
				Fn(SHL, PUSH(2) /* top of stack = Input */),
			),
		),
		stack.ExpectDepth(1),
	}

	for i := 0; i < 56; i++ { // note NOT 57
		var mul types.Bytecoder
		switch m := uint64(57 - i); {
		case m&(m-1) == 0:
			mul = Fn(SHL, PUSH(bits.Len64(m)-1))
		default:
			mul = Fn(MUL, PUSH(m))
		}

		factorial = append(
			factorial,
			// The actual JUMPDEST label is irrelevant, but the compiler insists
			// that they must be distinct.
			JUMPDEST(fmt.Sprintf("%d", i)), stack.SetDepth(1),
			mul,
		)
	}

	// If we'd bounded the loop above by 57 instead of 56 then we'd have a no-op
	// multiplication by 1 here, for 8 gas (PUSH + MUL). Removing it entirely
	// would require adjusting the earlier JUMP, negating any benefits, so we
	// can instead replace it with 3 extra JUMPDESTs for 3 gas.
	for i := 0; i < 4; i++ {
		factorial = append(factorial,
			JUMPDEST(fmt.Sprintf("a%d", i)), stack.SetDepth(1),
		)
	}

	return append(
		factorial,
		JUMPDEST("return"), stack.SetDepth(1),
		Fn(MSTORE, PUSH0),
		Fn(RETURN, PUSH0, PUSH(32)),

		JUMPDEST("revert"), stack.SetDepth(0),
		Fn(REVERT, PUSH0, PUSH0),
	)

	// ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
	// ========== STOP EDITING HERE ===========
	// ----------------------------------------
}

func main() {
	specopscli.Run(code())
}

// Stop unused imports being removed.
var (
	_ = stack.ExpectDepth(0)
	_ = common.Address{}
)

factorial_test.go

package main

import (
	"fmt"
	"testing"

	"github.com/holiman/uint256"
)

func TestFactorial(t *testing.T) {
	want := uint256.NewInt(1)
	c := code()
	for i := uint64(0); i < 18; i++ {
		t.Run(fmt.Sprintf("%d", i), func(t *testing.T) {
			bigI := uint256.NewInt(i)
			in := bigI.Bytes32()
			if i != 0 {
				want.Mul(want, bigI)
			}

			gotBuf, err := c.Run(append([]byte{0xd0, 0x97, 0xbc, 0x0d}, in[:]...))
			if err != nil {
				t.Fatal(err)
			}
			got := new(uint256.Int).SetBytes(gotBuf)

			if !got.Eq(want) {
				t.Errorf("%d! got %d; want %d", i, got, want)
			}
		})
	}
}

go.mod

module github.com/solidifylabs/specops

go 1.20

require (
	github.com/ethereum/go-ethereum v1.13.14
	github.com/gdamore/tcell/v2 v2.7.1
	github.com/google/go-cmp v0.5.9
	github.com/holiman/uint256 v1.2.4
	github.com/rivo/tview v0.0.0-20240225120200-5605142ca62e
	github.com/spf13/cobra v1.5.0
	golang.org/x/sync v0.5.0
)

require (
	github.com/bits-and-blooms/bitset v1.10.0 // indirect
	github.com/btcsuite/btcd/btcec/v2 v2.2.0 // indirect
	github.com/consensys/bavard v0.1.13 // indirect
	github.com/consensys/gnark-crypto v0.12.1 // indirect
	github.com/crate-crypto/go-kzg-4844 v0.7.0 // indirect
	github.com/decred/dcrd/dcrec/secp256k1/v4 v4.0.1 // indirect
	github.com/ethereum/c-kzg-4844 v0.4.0 // indirect
	github.com/gdamore/encoding v1.0.0 // indirect
	github.com/inconshreveable/mousetrap v1.0.0 // indirect
	github.com/lucasb-eyer/go-colorful v1.2.0 // indirect
	github.com/mattn/go-runewidth v0.0.15 // indirect
	github.com/mmcloughlin/addchain v0.4.0 // indirect
	github.com/rivo/uniseg v0.4.7 // indirect
	github.com/spf13/pflag v1.0.5 // indirect
	github.com/supranational/blst v0.3.11 // indirect
	golang.org/x/crypto v0.17.0 // indirect
	golang.org/x/exp v0.0.0-20231110203233-9a3e6036ecaa // indirect
	golang.org/x/sys v0.17.0 // indirect
	golang.org/x/term v0.17.0 // indirect
	golang.org/x/text v0.14.0 // indirect
	rsc.io/tmplfunc v0.0.3 // indirect
)