math/big: fix comment typo in natdiv.go

Comment in line 395:
[x₀ < S, so S - x₀ < 0; drop it]
Should be:
[x₀ < S, so S - x₀ > 0; drop it]

The proof is based on S - x₀ > 0, thus it's a typo of comment.

Fixes #68466

Change-Id: I68bb7cb909ba2bfe02a8873f74b57edc6679b72a
GitHub-Last-Rev: 40a2fc80cf22e97e0f535454a9b87b31b2e51421
GitHub-Pull-Request: golang/go#68487
Reviewed-on: https://go-review.googlesource.com/c/go/+/598855
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Keith Randall <khr@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@golang.org>
Auto-Submit: Keith Randall <khr@golang.org>

diff --git a/src/math/big/natdiv.go b/src/math/big/natdiv.go
index 2172eeca40a2dcc3b984f572a444069c72119a00..b55f9990cd5975cc220c4ac0b04c09cea7c41a26 100644 (file)
--- a/src/math/big/natdiv.go
+++ b/src/math/big/natdiv.go
@@ -392,7 +392,7 @@ Proof that q ≤ q̂:
              ≥ (1/y)·((x₁ - y₁ + 1)·S - x)    [above: q̂·y₁ ≥ x₁ - y₁ + 1]
              = (1/y)·(x₁·S - y₁·S + S - x)    [distribute S]
              = (1/y)·(S - x₀ - y₁·S)          [-x = -x₁·S - x₀]
-             > -y₁·S / y                      [x₀ < S, so S - x₀ < 0; drop it]
+             > -y₁·S / y                      [x₀ < S, so S - x₀ > 0; drop it]
              ≥ -1                             [y₁·S ≤ y]
 
        So q̂ - q > -1.