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(as.info)i386-Float

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Floating Point
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   All 80387 floating point types except packed BCD are supported.
(BCD support may be added without much difficulty).  These data types
are 16-, 32-, and 64- bit integers, and single (32-bit), double
(64-bit), and extended (80-bit) precision floating point.  Each
supported type has an instruction mnemonic suffix and a constructor
associated with it.  Instruction mnemonic suffixes specify the operand's
data type.  Constructors build these data types into memory.

   * Floating point constructors are `.float' or `.single', `.double',
     and `.tfloat' for 32-, 64-, and 80-bit formats.  These correspond
     to instruction mnemonic suffixes `s', `l', and `t'. `t' stands for
     80-bit (ten byte) real.  The 80387 only supports this format via
     the `fldt' (load 80-bit real to stack top) and `fstpt' (store
     80-bit real and pop stack) instructions.

   * Integer constructors are `.word', `.long' or `.int', and `.quad'
     for the 16-, 32-, and 64-bit integer formats.  The corresponding
     instruction mnemonic suffixes are `s' (single), `l' (long), and
     `q' (quad).  As with the 80-bit real format, the 64-bit `q' format
     is only present in the `fildq' (load quad integer to stack top)
     and `fistpq' (store quad integer and pop stack) instructions.

   Register to register operations should not use instruction mnemonic
suffixes.  `fstl %st, %st(1)' will give a warning, and be assembled as
if you wrote `fst %st, %st(1)', since all register to register
operations use 80-bit floating point operands. (Contrast this with
`fstl %st, mem', which converts `%st' from 80-bit to 64-bit floating
point format, then stores the result in the 4 byte location `mem')