SELECT size, pg_size_pretty(size), pg_size_pretty(-1 * size) FROM
    (VALUES (10::bigint), (1000::bigint), (1000000::bigint),
            (1000000000::bigint), (1000000000000::bigint),
            (1000000000000000::bigint)) x(size);
       size       | pg_size_pretty | pg_size_pretty 
------------------+----------------+----------------
               10 | 10 bytes       | -10 bytes
             1000 | 1000 bytes     | -1000 bytes
          1000000 | 977 kB         | -977 kB
       1000000000 | 954 MB         | -954 MB
    1000000000000 | 931 GB         | -931 GB
 1000000000000000 | 909 TB         | -909 TB
(6 rows)

SELECT size, pg_size_pretty(size), pg_size_pretty(-1 * size) FROM
    (VALUES (10::numeric), (1000::numeric), (1000000::numeric),
            (1000000000::numeric), (1000000000000::numeric),
            (1000000000000000::numeric),
            (10.5::numeric), (1000.5::numeric), (1000000.5::numeric),
            (1000000000.5::numeric), (1000000000000.5::numeric),
            (1000000000000000.5::numeric)) x(size);
        size        | pg_size_pretty | pg_size_pretty 
--------------------+----------------+----------------
                 10 | 10 bytes       | -10 bytes
               1000 | 1000 bytes     | -1000 bytes
            1000000 | 977 kB         | -977 kB
         1000000000 | 954 MB         | -954 MB
      1000000000000 | 931 GB         | -931 GB
   1000000000000000 | 909 TB         | -909 TB
               10.5 | 10.5 bytes     | -10.5 bytes
             1000.5 | 1000.5 bytes   | -1000.5 bytes
          1000000.5 | 977 kB         | -977 kB
       1000000000.5 | 954 MB         | -954 MB
    1000000000000.5 | 931 GB         | -931 GB
 1000000000000000.5 | 909 TB         | -909 TB
(12 rows)

SELECT size, pg_size_bytes(size) FROM
    (VALUES ('1'), ('123bytes'), ('1kB'), ('1MB'), (' 1 GB'), ('1.5 GB '),
            ('1TB'), ('3000 TB'), ('1e6 MB')) x(size);
   size   |  pg_size_bytes   
----------+------------------
 1        |                1
 123bytes |              123
 1kB      |             1024
 1MB      |          1048576
  1 GB    |       1073741824
 1.5 GB   |       1610612736
 1TB      |    1099511627776
 3000 TB  | 3298534883328000
 1e6 MB   |    1048576000000
(9 rows)

-- case-insensitive units are supported
SELECT size, pg_size_bytes(size) FROM
    (VALUES ('1'), ('123bYteS'), ('1kb'), ('1mb'), (' 1 Gb'), ('1.5 gB '),
            ('1tb'), ('3000 tb'), ('1e6 mb')) x(size);
   size   |  pg_size_bytes   
----------+------------------
 1        |                1
 123bYteS |              123
 1kb      |             1024
 1mb      |          1048576
  1 Gb    |       1073741824
 1.5 gB   |       1610612736
 1tb      |    1099511627776
 3000 tb  | 3298534883328000
 1e6 mb   |    1048576000000
(9 rows)

-- negative numbers are supported
SELECT size, pg_size_bytes(size) FROM
    (VALUES ('-1'), ('-123bytes'), ('-1kb'), ('-1mb'), (' -1 Gb'), ('-1.5 gB '),
            ('-1tb'), ('-3000 TB'), ('-10e-1 MB')) x(size);
   size    |   pg_size_bytes   
-----------+-------------------
 -1        |                -1
 -123bytes |              -123
 -1kb      |             -1024
 -1mb      |          -1048576
  -1 Gb    |       -1073741824
 -1.5 gB   |       -1610612736
 -1tb      |    -1099511627776
 -3000 TB  | -3298534883328000
 -10e-1 MB |          -1048576
(9 rows)

-- different cases with allowed points
SELECT size, pg_size_bytes(size) FROM
     (VALUES ('-1.'), ('-1.kb'), ('-1. kb'), ('-0. gb'),
             ('-.1'), ('-.1kb'), ('-.1 kb'), ('-.0 gb')) x(size);
  size  | pg_size_bytes 
--------+---------------
 -1.    |            -1
 -1.kb  |         -1024
 -1. kb |         -1024
 -0. gb |             0
 -.1    |             0
 -.1kb  |          -102
 -.1 kb |          -102
 -.0 gb |             0
(8 rows)

-- invalid inputs
SELECT pg_size_bytes('1 AB');
ERROR:  invalid size: "1 AB"
DETAIL:  Invalid size unit: "AB".
HINT:  Valid units are "bytes", "kB", "MB", "GB", and "TB".
SELECT pg_size_bytes('1 AB A');
ERROR:  invalid size: "1 AB A"
DETAIL:  Invalid size unit: "AB A".
HINT:  Valid units are "bytes", "kB", "MB", "GB", and "TB".
SELECT pg_size_bytes('1 AB A    ');
ERROR:  invalid size: "1 AB A    "
DETAIL:  Invalid size unit: "AB A".
HINT:  Valid units are "bytes", "kB", "MB", "GB", and "TB".
SELECT pg_size_bytes('9223372036854775807.9');
ERROR:  bigint out of range
SELECT pg_size_bytes('1e100');
ERROR:  bigint out of range
SELECT pg_size_bytes('1e1000000000000000000');
ERROR:  invalid size: "1e1000000000000000000"
SELECT pg_size_bytes('1 byte');  -- the singular "byte" is not supported
ERROR:  invalid size: "1 byte"
DETAIL:  Invalid size unit: "byte".
HINT:  Valid units are "bytes", "kB", "MB", "GB", and "TB".
SELECT pg_size_bytes('');
ERROR:  invalid size: ""
SELECT pg_size_bytes('kb');
ERROR:  invalid size: "kb"
SELECT pg_size_bytes('..');
ERROR:  invalid size: ".."
SELECT pg_size_bytes('-.');
ERROR:  invalid size: "-."
SELECT pg_size_bytes('-.kb');
ERROR:  invalid size: "-.kb"
SELECT pg_size_bytes('-. kb');
ERROR:  invalid size: "-. kb"
SELECT pg_size_bytes('.+912');
ERROR:  invalid size: ".+912"
SELECT pg_size_bytes('+912+ kB');
ERROR:  invalid size: "+912+ kB"
DETAIL:  Invalid size unit: "+ kB".
HINT:  Valid units are "bytes", "kB", "MB", "GB", and "TB".
SELECT pg_size_bytes('++123 kB');
ERROR:  invalid size: "++123 kB"