| -rw-r--r-- | doc/body.texi | 25 |
diff --git a/doc/body.texi b/doc/body.texi index 833828d..cb47139 100644 --- a/doc/body.texi +++ b/doc/body.texi @@ -318,6 +318,31 @@ qrshr _u O1 = O3 >> O4, O2 = O3 << (WORDSIZE - O4) qrshi _u O1 = O3 >> O4, O2 = O3 << (WORDSIZE - O4) @end example +These four operand ALU operations are only defined for float operands. + +@example +fmar _f _d O1 = O2 * O3 + O4 +fmai _f _d O1 = O2 * O3 + O4 +fmsr _f _d O1 = O2 * O3 - O4 +fmsi _f _d O1 = O2 * O3 - O4 +fnmar _f _d O1 = -O2 * O3 - O4 +fnmai _f _d O1 = -O2 * O3 - O4 +fnmsr _f _d O1 = -O2 * O3 + O4 +fnmsi _f _d O1 = -O2 * O3 + O4 +@end example + +These are a family of fused multiply-add instructions. +Note that @lightning{} does not handle rounding modes nor math exceptions. +Also note that not all backends provide a instruction for the equivalent +@lightning{} instruction presented above. Some are completely implemented +as fallbacks and some are composed of one or more instructions. For common +input this should not cause major issues, but note that when implemented by +the cpu, these are implemented as the multiplication calculated with infinite +precision, and after the addition step rounding is done. Due to this, For +specially crafted input different ports might show different output. When +implemented by the CPU, it is also possible to have exceptions that do +not happen if implemented as a fallback. + @item Unary ALU operations These accept two operands, the first must be a register and the second is a register if the @code{r} modifier is used, otherwise, |