Debugging

What I do

Cover debugging techniques for Constantine cryptographic code.

Quick Debugging

debugEcho

Use debugEcho instead of echo to avoid side-effect warnings in func procedures:

# Bad - echo has side effects, triggers compiler warnings in funcs
echo "Value: ", value

# Good - debugEcho is allowed in debug code
debugEcho "Value: ", value.toHex()

toHex for Quick Output

Use the toHex() functions for quick inspection of cryptographic values. You must import the corresponding IO module:

# Field elements (Fr, Fp)
import constantine/math/io/io_fields
debugEcho "Scalar: ", scalar.toHex()

# Elliptic curve points
import constantine/math/io/io_ec
debugEcho "Point: ", point.toHex()

# BigInts
import constantine/math/io/io_bigints
debugEcho "BigInt: ", bigInt.toHex()

# Extension fields (Fp2, Fp4, Fp6, Fp12)
import constantine/math/io/io_extfields
debugEcho "Fp2: ", fp2.toHex()

Conditional Debug Code

debug: Template

Code guarded by debug: from constantine/platforms/primitives.nim is only compiled when -d:CTT_DEBUG is defined:

from constantine/platforms/primitives import debug

debug:
  # This code only compiles with -d:CTT_DEBUG
  debugEcho "Debug info: ", value.toHex()
  doAssert someCondition, "Debug assertion failed"

Compile with:

nim c -d:CTT_DEBUG your_file.nim

Full Stack Traces

In release mode, code is optimized and stack traces may be incomplete. Use -d:linetrace for full stack traces:

# Full stack traces in release mode
nim c -d:release -d:linetrace your_file.nim

This is often necessary because:

• Release mode with -d:release is needed for realistic performance
• But -d:release removes debug info by default
• -d:linetrace restores full stack traces while keeping optimizations

Complex Debug Blocks

For complex debugging that can't use debugEcho, wrap in {.cast(noSideEffect).}:

{.cast(noSideEffect).}:
  block:
    # Complex debug code here
    echo "Debug info: ", someVar
    echo "More info: ", anotherVar.toHex()

Required Imports for toHex

Debugging Tips

1. Import the right IO module - toHex won't work without it
2. Start with toHex - Quickest way to see values
3. Use debugEcho - For simple prints in func procedures
4. Use debug: template - For code that should only exist in debug builds
5. Use {.cast(noSideEffect).} - For complex debug blocks in funcs
6. Use -d:CTT_DEBUG - For conditional compilation of debug code
7. Use -d:linetrace - For full stack traces in release mode