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fix: a time label's mantissa cannot reach its own radix

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`format_time()` picked its sub-second rung from the raw value, so three
significant figures of a value just under a rung's top rounded to 1000 and
`%.3g` wrote that as an exponent: a one-second tick computed as 0.9999999 s
read `1e+03ms`. The rung is now chosen by the rounded mantissa, which is the
same 999.5 check `format_si()` already made for the SI prefixes, and a value
that rounds to a whole second leaves the sub-second branch entirely.
This commit is contained in:
Martino Ferrari committed 2026-10-05 21:31:43 +02:00
1 parent c2c8c596f3
commit 58473db384
2 files changed
+21 -2
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tests/test_ticks.cpp
+12
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@@ -263,6 +263,18 @@ PLOT_TEST(format_time_never_lets_a_field_reach_its_radix) {
plot::format_time(86399.5, b, sizeof b); PLOT_CHECK(std::string(b) == "1d");
plot::format_time(86400.0, b, sizeof b); PLOT_CHECK(std::string(b) == "1d");
// A mantissa may not reach its own radix either: three significant figures of a value a
// hair under a rung's top round up to 1000, and `%.3g` writes that `1e+03`. A one-second
// tick computed as 0.9999999 s read `1e+03ms` on a live axis, which is where this was seen.
plot::format_time(0.9999999, b, sizeof b); PLOT_CHECK(std::string(b) == "1s");
plot::format_time(0.9995, b, sizeof b); PLOT_CHECK(std::string(b) == "1s");
plot::format_time(0.9994, b, sizeof b); PLOT_CHECK(std::string(b) == "999ms");
plot::format_time(0.9999999e-3, b, sizeof b); PLOT_CHECK(std::string(b) == "1ms");
plot::format_time(0.9994e-3, b, sizeof b); PLOT_CHECK(std::string(b) == "999\u00b5s");
plot::format_time(0.9999999e-6, b, sizeof b); PLOT_CHECK(std::string(b) == "1\u00b5s");
plot::format_time(0.9999999e-9, b, sizeof b); PLOT_CHECK(std::string(b) == "1ns");
plot::format_time(-0.9999999, b, sizeof b); PLOT_CHECK(std::string(b) == "-1s");
// Sweep the boundary neighbourhoods and check every emitted field.
const double values[] = {0.4, 0.9995, 1.0, 59.4, 59.4999, 59.5, 59.9, 60.0, 90.0, 119.5, 3599.4,
3599.5, 3599.9, 86399.4, 86399.5, 86399.9, 86400.0, 172800.0, -119.5,