Tippecanoe formatted every double it wrote through milo::dtoa_milo, a
vendored Grisu2. Grisu2 is fast, but it guarantees neither the shortest
digit string nor the correctly rounded one: it only guarantees that what
it prints parses back to the value it came from. In practice it prints a
digit more than necessary about 0.16% of the time, and picks a neighbor
of the correctly rounded digits about 32% of the time.
This ports Russ Cox's fpfmt (https://github.com/rsc/fpfmt) to C++ in
fpfmt/ and formats through it instead. fpfmt is both shortest and
correctly rounded, and it is faster:
full std::string formatting Grisu2 fpfmt speedup
random bit patterns 156.62 ns 66.83 ns 2.34x
geo coordinates 124.07 ns 58.62 ns 2.12x
short decimals 69.37 ns 49.16 ns 1.41x
small integers 44.18 ns 38.06 ns 1.16x
digit generation only Grisu2 fpfmt speedup
random bit patterns 90.07 ns 20.81 ns 4.33x
geo coordinates 80.64 ns 20.18 ns 4.00x
short decimals 55.61 ns 21.90 ns 2.54x
small integers 40.23 ns 22.50 ns 1.79x
(Intel Xeon @ 2.80GHz, g++ 13.3 -O3. `make fpfmt-bench` reproduces this,
and `./fpfmt-bench -check` reruns the correctness sweep, which is why
milo/dtoa_milo.h is kept even though nothing links it any more.)
The port is deliberately literal, so it can be diffed against fpfmt.go.
Its Short() agrees bit for bit with the Go original's on 445,640 values
covering powers of ten, small integers and reciprocals, subnormals, and
random bit patterns. Over 38.5 million values, fpfmt::dtoa always round
trips, is never longer than Grisu2's output, and is shorter 61,329 times.
Output is otherwise formatted exactly as before, including the choice
between plain and exponential notation, so 26 expected test outputs
change: some numbers lose digits (-26.170044999999999 becomes
-26.170045), and some have a corrected final digit (9.823748927348929e+55
becomes 9.823748927348928e+55). Every changed token was checked to parse
back to the identical double; none of the values themselves moved.
milo/milo.h, whose only job was to declare the C shim jsonpull calls, is
replaced by fpfmt/fpfmt.h, and the shim is renamed dtoa_shortest.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014wJRAuhMninQE4wK2TUfuZ
* Calculate a new antimeridian-adjusted bounding box
* Add antimeridian bounding box to pmtiles, dirtiles, and tile-join
* Don't take out-of-bounds latitudes into account in the adjusted bbox
* Update changelog
* Forgot to adjust tests after the last change
* Round coordinates instead of truncating them
* Update all the tests for coordinate rounding changes
* Curses, integer division still truncates
* Fix tests
* Also round instead of shifting when looking for no-op linetos
* Should I worry that the same change for moveto doesn't change any tests?
* Also round instead of shifting when scaling down to maxzoom resolution
* Replace another explicit shift, for origin point
* Round instead of shift when writing clipped geometries to the next zoom
* Fix low-zoom gridding and smaller-than-a-pixel checks
* Don't guess an excessively large maxzoom when there is only one feature
* Add a test for guessing the maxzoom of a single point
* Explicitly sort by index if no other order distinguishes features
* Another affected test
* add pmtiles.hpp from github.com/protomaps/PMTiles [#10]
* tippecanoe main writes pmtiles output. [#10]
* detect output format using suffix
* after mbtiles is done writing, replace with pmtiles based on map/image tables.
* add method to write_json for writing json sub-object.
* tippecanoe-decode reads pmtiles input. [#10]
* tile-join reads and writes pmtiles. [#10]
* pmtiles test suite for decode and tile-join [#10]
* add base GitHub CI action for compiling and test suite.
* update pmtiles.hpp with z>15 fix
* Fix some ordering problems with pmtiles decode
* Pmtiles should also pass the raw tiles tests
* Eradicate spaces from tileset metadata JSON fields
* Eradicate spaces from more test fixtures
* Update more tests
* Pmtiles tests pass now too
* Remove unnecessary sort (and make indent)
* Update changelog
* The allow-existing test for pmtiles needs -o, not -e
* Declare --allow-existing to be unsupported for pmtiles.
It was always a bad idea even for mbtiles.
Co-authored-by: Brandon Liu <bdon@bdon.org>
Claude