Re: Alternative variable length structure

On Thu, 08 Sep 2005 18:02:44 +0900, ITAGAKI Takahiro
<itagaki(dot)takahiro(at)lab(dot)ntt(dot)co(dot)jp> wrote:
+ * The length of varlena2 is encoded as follows:
+ *
+ * | First | Trailing | Total | Max |
+ * | byte | bytes | bits | length |
+ * +----------+----------+-------+---------+
+ * | 0******* | 0 | 7 | 127 |
+ * | 10****** | 1 | 14 | 16K -1 |
+ * | 110***** | 2 | 21 | 2M -1 |
+ * | 1110**** | 3 | 28 | 256M -1 |
+ * | 1111---- | 4 | 32 | 4G -1 |

With external and compression flags this would look like
* | ec0***** | 0 | 5 | 31 |
* | ec10**** | 1 | 12 | 4K -1 |
* | ec110*** | 2 | 19 | 512K -1 |
* | ec1110** | 3 | 26 | 64M -1 |
* | ec1111-- | 4 | 32 | 4G -1 |

Only a matter of taste, but I'd just waste one byte for sizes between 4K
and 512K and thus get a shorter table:
* | ec0***** | 0 | 5 | 31 |
* | ec10**** | 1 | 12 | 4K -1 |
* | ec110*** | 3 | 27 | 128M -1 |
* | ec111--- | 4 | 32 | 4G -1 |

And you get back that one byte for sizes between 64M and 128M :-)

Another possible tweak:
* | 0******* | 0 | 5 | 127 |
* | 1ec0**** | 1 | 12 | 4K -1 |
* | 1ec10*** | 3 | 27 | 128M -1 |
* | 1ec11--- | 4 | 32 | 4G -1 |

I.e. drop the flags for very short strings. If these flags are needed
for a string of size 32 to 127, then use a two byte header.

Servus
Manfred