Incorrect decoding of signed integers i8/i16

[peetzweg]

The decoding of some scale encoded signed integers values result in the wrong representation in js.
Generally scale encoded i8 and i16 value seem to work fine, however the edge cases, the value of 1 and i8::MAX and i16::MAX are decoded to the wrong representation in javascript.

This issue bubbles up in one form or another, see related issue section. How can we resolve this once and for all?

I've created a PR adding testcases for the broken decoding cases #5703.

• I'm submitting a ...

  • Bug report
  • Feature request
  • Support request
  • Other

• What is the current behavior and expected behavior?

// Scale encoded signed integers of value `1`
const bytes_1i8 = new Uint8Array([1]);
const bytes_1i16 = new Uint8Array([1, 0]);
const bytes_1i32 = new Uint8Array([1, 0, 0, 0]);
const bytes_1i128 = new Uint8Array([
    1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  ]);


api.createType("i8", bytes_1i8).toNumber(); // expected 1, actual -255 ❌
api.createType("i16", bytes_1i16).toNumber(); // expected 1, actual -65535 ❌
api.createType("i32", bytes_1i32).toNumber(); // expected 1, actual 1 ✅
api.createType("i128", bytes_1i128).toNumber(); // expected 1, actual 1 ✅


// Decoding MAX values for signed integers
const bytes_maxi8 = new Uint8Array([127]);
const bytes_maxi16 = new Uint8Array([255, 127]);
api.createType("i8", bytes_maxi8).toNumber(); // expected 127, actual -129 ❌
api.createType("i16", bytes_maxi16).toNumber(); // expected 32767, actual -32769 ❌


// SCALE encoded `0` value of `i8` and `i16`
const bytes_0i8 = new Uint8Array([0]);
const bytes_0i16 = new Uint8Array([0, 0]);
api.createType("i8", bytes_0i8).toNumber(); // expected 0, actual `Input too large. Found input with 9 bits, expected 8`  ❌
api.createType("i16", bytes_0i16).toNumber(); // expected 0, actual `Input too large. Found input with 17 bits, expected 16` ❌

Codesandbox Link

• Please tell us about your environment:

  • Version: @polkadot/[email protected]

    • Node.js
    • Browser
    • Other (limited support for other environments)

  • Language:

    • JavaScript
    • TypeScript (include tsc --version)
    • Other

Related Issues

• Unexpected values received for types i8 and i16 from ink! contract #5483

• Incorrect decoded return value of type Vec<(i16,i16)> use-ink/contracts-ui#508

• Decoding error & not correct decoding of returned types containing i16. use-ink/useink#105

[peetzweg]

I've probably identified the issues and written about it here: #5703 (comment)

[jacogr]

Closing, issues addressed at the util layer (test cases merged)

[polkadot-js-bot]

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