In general:

For minor changes to a function, copy the existing formatting.

When changing the style, commit that separately from other changes.

For new code and major changes to a function, switch to the official json-c style.

Official json-c style:

Aim for readability, not strict conformance to fixed style rules.

These rules are not comprehensive.  Look to existing code for guidelines.

Indentation is tab based, with continuations of long lines starting with tabs then spaces for alignment.

Try to line up components of continuation lines with corresponding part of the line above (i.e. "indent -lp" effect), but avoid excessive identation tha causes extra line wraps. 

 e.g. (T=tab, S=space):

TTTTsome_long_func_call(arg1, arg2,

TTTTSSSSSSSSSSSSSSSSSSSarg3, arg4);

TTTTsome_reallly_really_long_func_name(arg1,

TTTTTarg2, arg3, arg4);

There should be a space between "if"/"while" and the following parenthesis.

"case" lines are indented at the same level as the "switch" statement.

Commas are followed by a single space.

Include spaces around most non-unary, non-postfix operators, "=", "==', "&", "||", etc...

Function calls have no space between the name and the parenthesis.

Curly braces go on their own line.

Curly braces may be omitted.

Naming:

Words within function and variable names are separated with underscores.  Avoid camel case.

Prefer longer, more descriptive names, but not excessively so.  No single letter variable names.

Other:

Variables should be defined for the smallest scope needed.

Functions should be defined static when possible.

When possible, avoid exposing internals in the public API.