encoding/binary: removal of unnecessary boundary checks.

[lemmerelassal]

When creating a slice, e.g.: a 4 byte array can become optimized to 3 bytes only, resulting in a panic from the boundary check, which was experienced during decoding of LoRa packets.

Fixes issue #14808.

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This PR (HEAD: 801ef65) has been imported to Gerrit for code review.

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Patch Set 1:

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Message from Ian Lance Taylor:

Patch Set 1:

The description says that you are removing unnecessary boundary checks, but that's not what you are doing. You are changing the behavior of these methods when a short slice is passed in.

I don't see why that is desirable. The methods expect full size slices and should not be called on short slices. It's very easy for calling code to avoid calling these methods if they will not work.

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Message from Brad Fitzpatrick:

Patch Set 1: Code-Review-2

Also, these patterns are recognized by the compiler and optimized to single instructions.

This CL is almost certainly much slower than the original, in addition to changing the behavior.

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Message from Lemmer El Assal:

Patch Set 1:

Patch Set 1:

The description says that you are removing unnecessary boundary checks, but that's not what you are doing. You are changing the behavior of these methods when a short slice is passed in.

Go optimizes a []byte subslice of 4 (e.g.: buffer[4:9]) to shorter slices when the value is 0, which cause a panic.

Would it be preferrable to add this as a separate function altogether?

I don't see why that is desirable. The methods expect full size slices and should not be called on short slices. It's very easy for calling code to avoid calling these methods if they will not work.

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[gopherbot]

Message from Brad Fitzpatrick:

Patch Set 1:

Patch Set 1:

Patch Set 1:

The description says that you are removing unnecessary boundary checks, but that's not what you are doing. You are changing the behavior of these methods when a short slice is passed in.

Go optimizes a []byte subslice of 4 (e.g.: buffer[4:9]) to shorter slices when the value is 0, which cause a panic.

I don't understand. Which value?

Would it be preferrable to add this as a separate function altogether?

I don't know which function you want so I can't say.

I don't see why that is desirable. The methods expect full size slices and should not be called on short slices. It's very easy for calling code to avoid calling these methods if they will not work.

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[gopherbot]

Message from Go Bot:

Patch Set 1:

Congratulations on opening your first change. Thank you for your contribution!

Next steps:
Within the next week or so, a maintainer will review your change and provide
feedback. See https://golang.org/doc/contribute.html#review for more info and
tips to get your patch through code review.

Most changes in the Go project go through a few rounds of revision. This can be
surprising to people new to the project. The careful, iterative review process
is our way of helping mentor contributors and ensuring that their contributions
have a lasting impact.

During May-July and Nov-Jan the Go project is in a code freeze, during which
little code gets reviewed or merged. If a reviewer responds with a comment like
R=go1.11, it means that this CL will be reviewed as part of the next development
cycle. See https://golang.org/s/release for more details.

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