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From 0.9 stable spec, 5.3.1, table (no number), vector masking is referred to as having LSB. This suggests, yet does not require, that the mask field for each element is greater than bit-size 1.
From same spec, 4.6.1, each element mask bit is given an explicit location, as a single bit.
And yet, for individual operations, the LSB reference is still intact - such as in section 12.4 (Vector Integer Add-with-Carry / Subtract-with-Borrow Instructions).
This suggests some reformatting may be necessary regardless of the correct interpretation:
- If the single-bit-is-always-correct interpretation is to be asserted clearly, it would make sense to remove all of the ".LSB" references when discussing mask input/output fields.
- Otherwise, section 4.6.1 would need to be overhauled to be consistent with the idea of mask entries being multi-bit-per-element.
Thoughts?
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It is the case that mask elements are always one bit wide in this version of the spec. Removing the “.LSB” holdovers will improve clarity.
From 0.9 stable spec, 5.3.1, table (no number), vector masking is referred to as having LSB. This suggests, yet does not require, that the mask field for each element is greater than bit-size 1.
From same spec, 4.6.1, each element mask bit is given an explicit location, as a single bit.
And yet, for individual operations, the LSB reference is still intact - such as in section 12.4 (Vector Integer Add-with-Carry / Subtract-with-Borrow Instructions).
This suggests some reformatting may be necessary regardless of the correct interpretation:
- If the single-bit-is-always-correct interpretation is to be asserted clearly, it would make sense to remove all of the ".LSB" references when discussing mask input/output fields.
- Otherwise, section 4.6.1 would need to be overhauled to be consistent with the idea of mask entries being multi-bit-per-element.
Thoughts?
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Nick Knight
Hi Cohen,
I think the "LSB references" are carryovers from pre-0.9 versions, when MLEN > 1 was possible.
I can put together a PR to fix this later tonight, unless someone else gets to it sooner.
Best, Nick Knight
From 0.9 stable spec, 5.3.1, table (no number), vector masking is referred to as having LSB. This suggests, yet does not require, that the mask field for each element is greater than bit-size 1.
From same spec, 4.6.1, each element mask bit is given an explicit location, as a single bit.
And yet, for individual operations, the LSB reference is still intact - such as in section 12.4 (Vector Integer Add-with-Carry / Subtract-with-Borrow Instructions).
This suggests some reformatting may be necessary regardless of the correct interpretation:
- If the single-bit-is-always-correct interpretation is to be asserted clearly, it would make sense to remove all of the ".LSB" references when discussing mask input/output fields.
- Otherwise, section 4.6.1 would need to be overhauled to be consistent with the idea of mask entries being multi-bit-per-element.
Thoughts?
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Thank you Andrew and Nick.
To avoid having to repeat this question later, is it the intent moving forward (beyond "this version of the spec" being 0.9 stable) that this will hold true in the same format - at least, as of today?
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Nick Knight
I believe so: I am not aware of any proposals to reintroduce MLEN.
Thank you Andrew and Nick.
To avoid having to repeat this question later, is it the intent moving forward (beyond "this version of the spec" being 0.9 stable) that this will hold true in the same format - at least, as of today?
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Word of caution: there may be a utility/readability concern if the ".LSB" text is removed, only.
This would create a phrase
which can easily be misleading to the reader - while 'i' has the same value for all three terms, the first two indicate a SEW bit field, whereas the final term indicates a single bit.
Suggestions: include a reminder that v0[i] entries are a single bit under the opening comment in the code block ("Produce sum with carry."); Set a reminder at the bottom of the description section before starting the code text, or indicate a comment on the code line "#Vector-vector-bit".
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Word of caution: there may be a utility/readability concern if the ".LSB" text is removed, only.
This would create a phrase
which can easily be misleading to the reader - while 'i' has the same value for all three terms, the first two indicate a SEW bit field, whereas the final term indicates a single bit.
Suggestions: include a reminder that v0[i] entries are a single bit under the opening comment in the code block ("Produce sum with carry."); Set a reminder at the bottom of the description section before starting the code text, or indicate a comment on the code line "#Vector-vector-bit".
Or my preference a similar annotation that explicitly identifies it as a mast bit: vs2[i] + vs1[i] + v0[i].m
Or similar.
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On Wed, Sep 23, 2020 at 2:45 PM David Horner < ds2horner@...> wrote: Word of caution: there may be a utility/readability concern if the ".LSB" text is removed, only.
This would create a phrase
which can easily be misleading to the reader - while 'i' has the same value for all three terms, the first two indicate a SEW bit field, whereas the final term indicates a single bit.
Suggestions: include a reminder that v0[i] entries are a single bit under the opening comment in the code block ("Produce sum with carry."); Set a reminder at the bottom of the description section before starting the code text, or indicate a comment on the code line "#Vector-vector-bit".
Or my preference a similar annotation that explicitly identifies it as a mast bit: vs2[i] + vs1[i] + v0[i].m
Or similar.
👍
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Nick Knight
The existing draft used the notation v0.mask[i] in dozens of places to denote subscripting of a mask vector (bit granularity). I opted to use the existing notation uniformly, rather than switch to David's proposed v0[i].m . Happy to debate.
The .mask suffix was not previously used in unsubscripted contexts, and I did not introduce it there.
Best, Nick Knight
On Wed, Sep 23, 2020 at 3:11 PM Andrew Waterman < andrew@...> wrote:
On Wed, Sep 23, 2020 at 2:45 PM David Horner < ds2horner@...> wrote: Word of caution: there may be a utility/readability concern if the ".LSB" text is removed, only.
This would create a phrase
which can easily be misleading to the reader - while 'i' has the same value for all three terms, the first two indicate a SEW bit field, whereas the final term indicates a single bit.
Suggestions: include a reminder that v0[i] entries are a single bit under the opening comment in the code block ("Produce sum with carry."); Set a reminder at the bottom of the description section before starting the code text, or indicate a comment on the code line "#Vector-vector-bit".
Or my preference a similar annotation that explicitly identifies it as a mast bit: vs2[i] + vs1[i] + v0[i].m
Or similar.
👍
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You got my thumbs up!
Definitely "something similar" and better that my more cryptic
proposal.
Thanks you Cohen for raising these concerns and Nick for moving
this along so quickly.
On 2020-09-24 12:48 a.m., Nick Knight
wrote:
toggle quoted message
Show quoted text
The existing draft used the notation v0.mask[i] in dozens of
places to denote subscripting of a mask vector (bit
granularity). I opted to use the existing notation uniformly,
rather than switch to David's proposed v0[i].m . Happy to
debate.
The .mask
suffix was not previously used in unsubscripted contexts, and
I did not introduce it there.
Best,
Nick Knight
On Wed, Sep 23, 2020 at 3:11
PM Andrew Waterman < andrew@...> wrote:
On Wed, Sep 23, 2020 at
2:45 PM David Horner < ds2horner@...>
wrote:
Word of caution: there may be a
utility/readability concern if the ".LSB" text
is removed, only.
This would create a phrase
which can easily be misleading to the reader
- while 'i' has the same value for all three
terms, the first two indicate a SEW bit field,
whereas the final term indicates a single bit.
Suggestions: include a reminder that v0[i]
entries are a single bit under the opening
comment in the code block ("Produce sum with
carry."); Set a reminder at the bottom of the
description section before starting the code
text, or indicate a comment on the code line
"#Vector-vector-bit".
Or my preference a similar annotation
that explicitly identifies it as a mast bit:
vs2[i]
+ vs1[i] + v0[i].m
Or
similar.
👍
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