mirror/nasm
2
0
Fork 0
mirror of https://github.com/netwide-assembler/nasm.git synced 2025-03-31 18:20:22 +08:00
Code Issues Packages Projects Releases Wiki Activity

nasmdoc: document the __float*__ operators

Browse Source
This commit is contained in:
H. Peter Anvin 2007-09-24 12:44:38 -07:00
parent dc467ba8af
commit ea043ef039
1 changed files with 29 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

39
doc/nasmdoc.src
View File

@ -1392,17 +1392,20 @@ when they are operands to \c{dw}.
\S{fltconst} \I{floating-point, constants}Floating-Point Constants
\i{Floating-point} constants are acceptable only as arguments to
\i\c{DW}, \i\c{DD}, \i\c{DQ}, \i\c{DT}, and \i\c{DO}. They are
expressed in the traditional form: digits, then a period, then
optionally more digits, then optionally an \c{E} followed by an
exponent. The period is mandatory, so that NASM can distinguish
between \c{dd 1}, which declares an integer constant, and \c{dd 1.0}
which declares a floating-point constant.
\i\c{DW}, \i\c{DD}, \i\c{DQ}, \i\c{DT}, and \i\c{DO}, or as arguments
to the special operators \i\c{__float16__}, \i\c{__float32__},
\i\c{__float64__}, \i\c{__float80m__}, \i\c{__float80e__},
\i\c{__float128l__}, and \i\c{__float128h__}.
NASM also support C99-style hexadecimal floating-point: \c{0x},
hexadecimal digits, period, optionally more hexadeximal digits, then
optionally a \c{P} followed by a \e{binary} (not hexadecimal) exponent
in decimal notation.
Floating-point constants are expressed in the traditional form:
digits, then a period, then optionally more digits, then optionally an
\c{E} followed by an exponent. The period is mandatory, so that NASM
can distinguish between \c{dd 1}, which declares an integer constant,
and \c{dd 1.0} which declares a floating-point constant. NASM also
support C99-style hexadecimal floating-point: \c{0x}, hexadecimal
digits, period, optionally more hexadeximal digits, then optionally a
\c{P} followed by a \e{binary} (not hexadecimal) exponent in decimal
notation.
Some examples:
@ -1415,6 +1418,22 @@ Some examples:
\c dt 3.141592653589793238462 ; pi
\c do 1.e+4000 ; IEEE quad precision
The special operators are used to produce floating-point numbers in
other contexts. They produce the binary representation of a specific
floating-point number as an integer, and can use anywhere integer
constants are used in an expression. \c{__float80m__} and
\c{__float80e__} produce the 64-bit mantissa and 16-bit exponent of an
80-bit floating-point number, and \c{__float128l__} and
\c{__float128h__} produce the lower and upper 64-bit half of a 128-bit
floating-point number, respectively.
For example:
\c mov rax,__float64__(3.141592653589793238462)
... would assign the binary representation of pi as a 64-bit floating
point number into \c{RAX}.
NASM cannot do compile-time arithmetic on floating-point constants.
This is because NASM is designed to be portable - although it always
generates code to run on x86 processors, the assembler itself can