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Claude
7127e49c86
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
28 lines
1.4 KiB
Plaintext
28 lines
1.4 KiB
Plaintext
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