fs/bcachefs/varint.c

   1 // SPDX-License-Identifier: GPL-2.0
   2
   3 #include <linux/bitops.h>
   4 #include <linux/math.h>
   5 #include <linux/string.h>
   6 #include <linux/unaligned.h>
   7
   8 #ifdef CONFIG_VALGRIND
   9 #include <valgrind/memcheck.h>
  10 #endif
  11
  12 #include "varint.h"
  13
  14 /**
  15  * bch2_varint_encode - encode a variable length integer
  16  * @out:        destination to encode to
  17  * @v:          unsigned integer to encode
  18  * Returns:     size in bytes of the encoded integer - at most 9 bytes
  19  */
  20 int bch2_varint_encode(u8 *out, u64 v)
  21 {
  22         unsigned bits = fls64(v|1);
  23         unsigned bytes = DIV_ROUND_UP(bits, 7);
  24         __le64 v_le;
  25
  26         if (likely(bytes < 9)) {
  27                 v <<= bytes;
  28                 v |= ~(~0 << (bytes - 1));
  29                 v_le = cpu_to_le64(v);
  30                 memcpy(out, &v_le, bytes);
  31         } else {
  32                 *out++ = 255;
  33                 bytes = 9;
  34                 put_unaligned_le64(v, out);
  35         }
  36
  37         return bytes;
  38 }
  39
  40 /**
  41  * bch2_varint_decode - encode a variable length integer
  42  * @in:         varint to decode
  43  * @end:        end of buffer to decode from
  44  * @out:        on success, decoded integer
  45  * Returns:     size in bytes of the decoded integer - or -1 on failure (would
  46  * have read past the end of the buffer)
  47  */
  48 int bch2_varint_decode(const u8 *in, const u8 *end, u64 *out)
  49 {
  50         unsigned bytes = likely(in < end)
  51                 ? ffz(*in & 255) + 1
  52                 : 1;
  53         u64 v;
  54
  55         if (unlikely(in + bytes > end))
  56                 return -1;
  57
  58         if (likely(bytes < 9)) {
  59                 __le64 v_le = 0;
  60
  61                 memcpy(&v_le, in, bytes);
  62                 v = le64_to_cpu(v_le);
  63                 v >>= bytes;
  64         } else {
  65                 v = get_unaligned_le64(++in);
  66         }
  67
  68         *out = v;
  69         return bytes;
  70 }
  71
  72 /**
  73  * bch2_varint_encode_fast - fast version of bch2_varint_encode
  74  * @out:        destination to encode to
  75  * @v:          unsigned integer to encode
  76  * Returns:     size in bytes of the encoded integer - at most 9 bytes
  77  *
  78  * This version assumes it's always safe to write 8 bytes to @out, even if the
  79  * encoded integer would be smaller.
  80  */
  81 int bch2_varint_encode_fast(u8 *out, u64 v)
  82 {
  83         unsigned bits = fls64(v|1);
  84         unsigned bytes = DIV_ROUND_UP(bits, 7);
  85
  86         if (likely(bytes < 9)) {
  87                 v <<= bytes;
  88                 v |= ~(~0U << (bytes - 1));
  89         } else {
  90                 *out++ = 255;
  91                 bytes = 9;
  92         }
  93
  94         put_unaligned_le64(v, out);
  95         return bytes;
  96 }
  97
  98 /**
  99  * bch2_varint_decode_fast - fast version of bch2_varint_decode
 100  * @in:         varint to decode
 101  * @end:        end of buffer to decode from
 102  * @out:        on success, decoded integer
 103  * Returns:     size in bytes of the decoded integer - or -1 on failure (would
 104  * have read past the end of the buffer)
 105  *
 106  * This version assumes that it is safe to read at most 8 bytes past the end of
 107  * @end (we still return an error if the varint extends past @end).
 108  */
 109 int bch2_varint_decode_fast(const u8 *in, const u8 *end, u64 *out)
 110 {
 111 #ifdef CONFIG_VALGRIND
 112         VALGRIND_MAKE_MEM_DEFINED(in, 8);
 113 #endif
 114         u64 v = get_unaligned_le64(in);
 115         unsigned bytes = ffz(*in) + 1;
 116
 117         if (unlikely(in + bytes > end))
 118                 return -1;
 119
 120         if (likely(bytes < 9)) {
 121                 v >>= bytes;
 122                 v &= ~(~0ULL << (7 * bytes));
 123         } else {
 124                 v = get_unaligned_le64(++in);
 125         }
 126
 127         *out = v;
 128         return bytes;
 129 }