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test/float_lit2: fix expressions in comment

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The change corrects the values of the largest float32 value (f1) and the
value of the halfway point between f1 and the next, overflow value (f2).

Fixes #17012

Change-Id: Idaf9997b69d61fafbffdb980d751c9857732e14d
Reviewed-on: https://go-review.googlesource.com/29171
Reviewed-by: Robert Griesemer <gri@golang.org>
This commit is contained in:
Jan Mercl 2016-09-14 13:17:37 +02:00 committed by Robert Griesemer
parent 7f583a4d72
commit 2e675142dd
1 changed files with 2 additions and 2 deletions
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4
test/float_lit2.go
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@ -13,12 +13,12 @@ import (
"math"
)
// The largest exact float32 is f₁ = (1+(1-2²³))×2¹²⁷ = (1-2²⁴)×2¹²⁸ = 2¹²⁸ - 2¹⁰⁴.
// The largest exact float32 is f₁ = (1+1-1/2²³)×2¹²⁷ = (2-2⁻²³)×2¹²⁷ = 2¹²⁸ - 2¹⁰⁴.
// The next float32 would be f₂ = (1+1)×2¹²⁷ = 1×2¹²⁸, except that exponent is out of range.
// Float32 conversion rounds to the nearest float32, rounding to even mantissa:
// between f₁ and f₂, values closer to f₁ round to f₁ and values closer to f₂ are rejected as out of range.
// f₁ is an odd mantissa, so the halfway point (f₁+f₂)/2 rounds to f₂ and is rejected.
// The halfway point is (f₁+f₂)/2 = 2¹²⁸ - 2¹⁰⁵.
// The halfway point is (f₁+f₂)/2 = 2¹²⁸ - 2¹⁰³.
//
// The same is true of float64, with different constants: s/24/53/ and s/128/1024/.