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How To Override Methods Compiled Code

In some rare cases you might want to use low level Bitcoin script to write a smart contracts method. This is usually done for optimization of the scrip size. To achieve this currently, you have to edit the transpiled .scrypt files under your projects artifacts directory.

To make this a bit easier, you can re-use the code inside the optimizations/ directory in scrypt-ts-lib.

Inside this directory, there is a shell script named apply_asm_optim.sh. In this script, you can specify the source files where substitution with a custom bitcoin script should occur.

Let's take a quick look at how this is applied in scrypt-ts-lib for three source files:

# BN256
apply artifacts/src/ec/bn256.scrypt optimizations/ec/bn256

# SECP256K1
apply artifacts/src/ec/secp256k1.scrypt optimizations/ec/secp256k1

# SECP256R1
apply artifacts/src/ec/secp256r1.scrypt optimizations/ec/secp256r1

For instance, let's consider the content of optimizations/ec/bn256:

_addCurvePoints.asm
doubleCurvePoint.asm
lineFuncAdd.asm
lineFuncDouble.asm
modInverseBranchlessP.asm
mulFQ12.asm
mulLine.asm
squareFQ12.asm

The name of each file corresponds to a function in the specified .scrypt source file (bn256.scrypt for this example). The files contain the actual bitcoin script in ASM format:

OP_3 OP_PICK 11 OP_PICK OP_MUL 12 OP_PICK OP_4 OP_PICK OP_MUL OP_ADD OP_3 OP_PICK 12 OP_PICK OP_MUL OP_5 OP_PICK 14 OP_PICK OP_MUL OP_SUB OP_7 OP_PICK 11 OP_PICK OP_MUL 12 OP_PICK OP_8 OP_PICK OP_MUL OP_ADD OP_7 OP_PICK 12 OP_PICK OP_MUL OP_9 OP_PICK 14 OP_PICK OP_MUL OP_SUB OP_3 OP_ROLL OP_ROT OP_ADD OP_ROT OP_ROT OP_ADD OP_4 OP_PICK 11 OP_PICK 13 OP_PICK OP_8 OP_PICK OP_DUP OP_3 OP_PICK OP_MUL OP_2 OP_PICK OP_5 OP_PICK OP_MUL OP_ADD OP_SWAP OP_ROT OP_MUL OP_3 OP_ROLL OP_3 ...

Please note that it is crucial to run apply_asm_optim.sh after each project build. To make this process more convenient, you can modify the build script in package.json:

"scripts": {
    "build": "tsc && npm run apply-optim",
    "apply-optim": "sh optimizations/apply_asm_optim.sh",
    ...

Now, after every build, the script optimizations will be applied.

:::note Please bear in mind that modifying the contract's script code may cause inconsistencies between the on-chain and local execution (methods TS code) behavior. Once you modify the Bitcoin script, it is your responsibility to keep the two versions functionally equivalent. :::