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nexedi
MariaDB
Commits
ee898804
Commit
ee898804
authored
Aug 16, 2004
by
konstantin@mysql.com
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A desperate attempt to comment one place where we do conversions.
parent
f08912e5
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sql/field.cc
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sql/field.cc
View file @
ee898804
...
@@ -2332,6 +2332,33 @@ String *Field_double::val_str(String *val_buffer,
...
@@ -2332,6 +2332,33 @@ String *Field_double::val_str(String *val_buffer,
if
(
dec
>=
NOT_FIXED_DEC
)
if
(
dec
>=
NOT_FIXED_DEC
)
{
{
/*
Let's try to pretty print a floating point number. Here we use
'%-*.*g' conversion string:
'-' stands for left-padding with spaces, if such padding will take
place
'*' is a placeholder for the first argument, field_length, and
signifies minimal width of result string. If result is less than
field length it will be space-padded. Note, however, that we'll not
pass spaces to Field_string::store(const char *, ...), due to
strcend in the next line.
'.*' is a placeholder for DBL_DIG and defines maximum number of
significant digits in the result string. DBL_DIG is a hardware
specific C define for maximum number of decimal digits of a floating
point number, such that rounding to hardware floating point
representation and back to decimal will not lead to loss of
precision. I.e if DBL_DIG is 15, number 123456789111315 can be
represented as double without precision loss. As one can judge from
this description, chosing DBL_DIG here is questionable, especially
because it introduces a system dependency.
'g' means that conversion will use [-]ddd.ddd (conventional) style,
and fall back to [-]d.ddde[+|i]ddd (scientific) style if there is no
enough space for all digits.
Maximum length of result string (not counting spaces) is (I guess)
DBL_DIG + 8, where 8 is 1 for sign, 1 for decimal point, 1 for
exponent sign, 1 for exponent, and 4 for exponent value.
XXX: why do we use space-padding and trim spaces in the next line?
*/
sprintf
(
to
,
"%-*.*g"
,(
int
)
field_length
,
DBL_DIG
,
nr
);
sprintf
(
to
,
"%-*.*g"
,(
int
)
field_length
,
DBL_DIG
,
nr
);
to
=
strcend
(
to
,
' '
);
to
=
strcend
(
to
,
' '
);
}
}
...
...
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