Comment 1 for bug 1680333

see https://www.w3.org/TR/SVG/types.html#Precision

"
Unless stated otherwise for a particular attribute or property, a <number> has the capacity for at least a single-precision floating point number and has a range (at a minimum) of -3.4e+38F to +3.4e+38F.

It is recommended that higher precision floating point storage and computation be performed on operations such as coordinate system transformations to provide the best possible precision and to prevent round-off errors.

Conforming High-Quality SVG Viewers are required to use at least double-precision floating point for intermediate calculations on certain numerical operations.
"

I think even if most codepaths uses single precision floats, some might use double precision (for paths, probably), and that lib2geom is templatable for precision. (see also the IEEE 754-2008 standard for conversions)