ecvt.3

UNIX v6源代码 这几乎是最经典的unix版本 unix操作系统设计和莱昂氏unix源代码分析都是用的该版

.th ECVT III 4/30/73
.sh NAME
ecvt, fcvt \*- output conversion
.sh SYNOPSIS
.ft B
jsr	pc,ecvt
.s3
jsr	pc,fcvt
.s3
char *ecvt(value, ndigit, decpt, sign)
.br
double value;
.br
int ndigit, *decpt, *sign;
.s3
char *fcvt(value, ndigit, decpt, sign)
.br
.li
...
.ft R
.sh DESCRIPTION
.it Ecvt
is called with a floating point number in fr0.
.s3
On exit, the number has been converted into a
string of ascii digits in a buffer pointed to by r0.
The number of digits produced is controlled
by a global variable \fI\*_ndigits\fR.
.s3
Moreover, the position of the decimal point is
contained in r2: r2=0 means the d.p. is at the
left hand end of the string of digits;
r2>0 means the d.p. is within or to the right
of the string.
.s3
The sign of the number is indicated by r1 (0 for +; 1 for \*-).
.s3
The low order digit has suffered decimal rounding
(i. e. may have been carried into).
.s3
From C,
the
.it value
is converted and a pointer to a null-terminated
string of \fIndigit\fR digits is returned.
The position of the decimal point is stored indirectly
through \fIdecpt\fR (negative means to the left of the
returned digits).
If the sign of the result is negative,
the word pointed to by \fIsign\fR is non-zero, otherwise
it is zero.
.s3
\fIFcvt\fR is identical to \fIecvt\fR, except that the correct digit
been rounded for F-style output of the number
of digits specified by \fI\(*_ndigits\fR.
.sh "SEE ALSO"
printf (III)
.sh BUGS