[PATCH 1/2] docs: lzo: fix first byte interpretation off-by-one

[PATCH 1/2] docs: lzo: fix first byte interpretation off-by-one

[C. Masloch]

There was an error in the description of the initial byte's
interpretation. While "18..21" was listed as  "copy 0..3 literals",
it should actually be interpreted as "copy 1..4 literals".

The "byte - 17" part is correct. 17 would encode copying "zero"
literals, but does not occur. 18 encodes copying 1 literal,
19 then 2 literals, 20 for 3 literals, 21 for 4 literals.
The description should read "18..21" as "copy 1..4 literals".
Likewise, 22 indicates "copying 5 literals", not "4 literals".
However, the state is indeed always set to "byte - 17" (which
for 21 results in 4 too).

Signed-off-by: C. Masloch <pushbx@ulukai.org>
---
 Documentation/lzo.txt | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/Documentation/lzo.txt b/Documentation/lzo.txt
index ca9833289..f839d104d 100644
--- a/Documentation/lzo.txt
+++ b/Documentation/lzo.txt
@@ -108,12 +108,12 @@ Byte sequences
                 (version 1 only).
                 Otherwise, the bitstream version is 0.
 
-      18..21  : copy 0..3 literals
-                state = (byte - 17) = 0..3  [ copy <state> literals ]
+      18..21  : copy 1..4 literals
+                state = (byte - 17) = 1..4  [ copy <state> literals ]
                 skip byte
 
       22..255 : copy literal string
-                length = (byte - 17) = 4..238
+                length = (byte - 17) = 5..238
                 state = 4 [ don't copy extra literals ]
                 skip byte
 
-- 
2.26.2

[PATCH 2/2] docs: lzo: fix incorrect statement about distance zero for EOS

[C. Masloch]

The encoded distance bits are zero, but the distance that is
calculated from this is actually equal to 16384. So correct
this statement to read that the 0001HLLL instruction means
EOS when a distance of 16384 is seen. This matches with the
description of the instruction itself later on.

Signed-off-by: C. Masloch <pushbx@ulukai.org>
---
 Documentation/lzo.txt | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/Documentation/lzo.txt b/Documentation/lzo.txt
index f839d104d..dc9e876cb 100644
--- a/Documentation/lzo.txt
+++ b/Documentation/lzo.txt
@@ -65,9 +65,9 @@ Description
   generally encoded in the last two bits of the instruction but may also be
   taken from the last two bits of an extra operand (eg: distance).
 
-  End of stream is declared when a block copy of distance 0 is seen. Only one
-  instruction may encode this distance (0001HLLL), it takes one LE16 operand
-  for the distance, thus requiring 3 bytes.
+  End of stream is declared when a block copy of distance 16384 is seen,
+  encoded in a certain instruction (0001HLLL) with the H and D bits all zero.
+  It takes one LE16 operand for the distance, thus requiring 3 bytes.
 
   .. important::
 
-- 
2.26.2

Re: [PATCH 1/2] docs: lzo: fix first byte interpretation off-by-one

[Dave Rodgman]

Your update looks correct to me, thanks.

Dave

On 22/05/2020, 15:11, "C. Masloch" <pushbx@ulukai.org> wrote:

    There was an error in the description of the initial byte's
    interpretation. While "18..21" was listed as  "copy 0..3 literals",
    it should actually be interpreted as "copy 1..4 literals".

    The "byte - 17" part is correct. 17 would encode copying "zero"
    literals, but does not occur. 18 encodes copying 1 literal,
    19 then 2 literals, 20 for 3 literals, 21 for 4 literals.
    The description should read "18..21" as "copy 1..4 literals".
    Likewise, 22 indicates "copying 5 literals", not "4 literals".
    However, the state is indeed always set to "byte - 17" (which
    for 21 results in 4 too).

    Signed-off-by: C. Masloch <pushbx@ulukai.org>
    ---
     Documentation/lzo.txt | 6 +++---
     1 file changed, 3 insertions(+), 3 deletions(-)

    diff --git a/Documentation/lzo.txt b/Documentation/lzo.txt
    index ca9833289..f839d104d 100644
    --- a/Documentation/lzo.txt
    +++ b/Documentation/lzo.txt
    @@ -108,12 +108,12 @@ Byte sequences
                     (version 1 only).
                     Otherwise, the bitstream version is 0.

    -      18..21  : copy 0..3 literals
    -                state = (byte - 17) = 0..3  [ copy <state> literals ]
    +      18..21  : copy 1..4 literals
    +                state = (byte - 17) = 1..4  [ copy <state> literals ]
                     skip byte

           22..255 : copy literal string
    -                length = (byte - 17) = 4..238
    +                length = (byte - 17) = 5..238
                     state = 4 [ don't copy extra literals ]
                     skip byte

    --
    2.26.2


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Re: [PATCH 2/2] docs: lzo: fix incorrect statement about distance zero for EOS

[Dave Rodgman]

Looks good to me, thanks

Dave

On 22/05/2020, 15:11, "C. Masloch" <pushbx@ulukai.org> wrote:

    The encoded distance bits are zero, but the distance that is
    calculated from this is actually equal to 16384. So correct
    this statement to read that the 0001HLLL instruction means
    EOS when a distance of 16384 is seen. This matches with the
    description of the instruction itself later on.

    Signed-off-by: C. Masloch <pushbx@ulukai.org>
    ---
     Documentation/lzo.txt | 6 +++---
     1 file changed, 3 insertions(+), 3 deletions(-)

    diff --git a/Documentation/lzo.txt b/Documentation/lzo.txt
    index f839d104d..dc9e876cb 100644
    --- a/Documentation/lzo.txt
    +++ b/Documentation/lzo.txt
    @@ -65,9 +65,9 @@ Description
       generally encoded in the last two bits of the instruction but may also be
       taken from the last two bits of an extra operand (eg: distance).

    -  End of stream is declared when a block copy of distance 0 is seen. Only one
    -  instruction may encode this distance (0001HLLL), it takes one LE16 operand
    -  for the distance, thus requiring 3 bytes.
    +  End of stream is declared when a block copy of distance 16384 is seen,
    +  encoded in a certain instruction (0001HLLL) with the H and D bits all zero.
    +  It takes one LE16 operand for the distance, thus requiring 3 bytes.

       .. important::

    --
    2.26.2


IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. If you are not the intended recipient, please notify the sender immediately and do not disclose the contents to any other person, use it for any purpose, or store or copy the information in any medium. Thank you.