9.15.9 Floating Point

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')