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dump[2]: avoid misleading rounding of numbers

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This commit is contained in:
Lars Mueller
2025-04-21 19:50:34 +02:00
committed by Lars Müller
parent f4285a59ac
commit 98b2edeb11
2 changed files with 16 additions and 1 deletions
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10
builtin/common/misc_helpers.lua
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@@ -7,7 +7,15 @@ local math = math
local function basic_dump(o) local function basic_dump(o)
local tp = type(o) local tp = type(o)
if tp == "number" then if tp == "number" then
return tostring(o) local s = tostring(o)
if tonumber(s) == o then
return s
end
-- Prefer an exact representation over a compact representation.
-- e.g. basic_dump(0.3) == "0.3",
-- but basic_dump(0.1 + 0.2) == "0.30000000000000004"
-- so the user can see that 0.1 + 0.2 ~= 0.3
return string.format("%.17g", o)
elseif tp == "string" then elseif tp == "string" then
return string.format("%q", o) return string.format("%q", o)
elseif tp == "boolean" then elseif tp == "boolean" then

7
builtin/common/tests/misc_helpers_spec.lua
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@@ -230,3 +230,10 @@ describe("math", function()
assert.equal(0, math.round(-0.49999999999999994)) assert.equal(0, math.round(-0.49999999999999994))
end) end)
end) end)
describe("dump", function()
it("avoids misleading rounding of floating point numbers", function()
assert.equal("0.3", dump(0.3))
assert.equal("0.30000000000000004", dump(0.1 + 0.2))
end)
end)