/*****************************************************************************Copyright ( c ) 2024 Kristian Nielsen . This program is free software ; you can redistribute it and / or modify it under the terms of the GNU General Public License as published by the Free Software Foundation ; version 2 of the License . This program is distributed in the hope that it will be useful , but WITHOUT ANY WARRANTY ; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE . See the GNU General Public License for more details . You should have received a copy of the GNU General Public License along with this program ; if not , write to the Free Software Foundation , Inc . , 51 Franklin Street , Fifth Floor , Boston , MA 02110 - 1335 USA /* Reading and writing of compressed integers . Created 2024 - 10 - 01 Kristian Nielsen < knielsen @ knielsen - hq . org > #ifndef MY_COMPR_INT_H#define MY_COMPR_INT_H#include "my_bit.h" #include <stdint.h>#include <utility>/* Read and write compressed ( up to ) 64 - bit integers . A 64 - bit number is encoded with 1 - 9 bytes . The 3 first bits stores a tag that determines the number of bytes used , and the encoding is written in little - endian format as ( TAG | ( NUMBER < < 3 ) ) . The tag is the number of bytes used minus 1 , except that 7 denotes 9 bytes used ( numbers are never encoded with 8 bytes ) . For example : Number Encoding 0 0 x00 0 x1f 0 xf8 ( 0 | ( 0 x1f < < 3 ) ) 0 x20 0 x01 0 x01 0 xf6 0 xb1 0 x07 0 xd34a 0 x52 0 x9a 0 x06 0 x1fffffffffffff 0 xfe 0 xff 0 xff 0 xff 0 xff 0 xff 0 xff 0 x20000000000000 0 x07 0 x00 0 x00 0 x00 0 x00 0 x00 0 x00 0 x01 0 x00 0 xffffffffffffffff 0 xff 0 xff 0 xff 0 xff 0 xff 0 xff 0 xff 0 xff 0 x07 The main advantage over something like base - 128 compression ( also called varint ) is that the encoding and decoding can happen with just a single conditional jump to determine if one or two 64 - bit words are involved ( or even no or only well - predicted conditional jump if unaligned reads / writes and buffer padding can be assumed ) . #define COMPR_INT_MAX32 5 #define COMPR_INT_MAX64 9 #define COMPR_INT_MAX COMPR_INT_MAX64/* Write compressed unsigned integer */ extern unsigned char *compr_int_write(unsigned char *p, uint64_t v);/* Read compressed integer . Returns a pair of the value read and the incremented pointer . extern std::pair<uint64_t, const unsigned char *>const unsigned char *p);#endif /* MY_COMPR_INT_H */
Messung V0.5 in Prozent C=93 H=100 G=96
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(vorverarbeitet am 2026-10-08)
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