Intel i86W Manual page 94

FLOATING-POINT INSTRUCTIONS
starting double-precision operations, and vice versa. For the adventuresome, the rules for
mixing precisions follow:
• Single to Double Transitions. When a pipelined multiplier operation with double-
precision inputs is executed and the previous multiplier operation was pipelined with
single-precision inputs, the third previous (last stage) result is stored, and the previ-
ous operation (first stage) is advanced to the second stage (now the last stage). The
second previous operation (old second stage) is discarded. The next pipelined multi-
plier operation stores the single-precision result.
• Double to Single Transitions. When a pipelined multiplier operation with single-
precision inputs is executed and the previous mUltiplier operation was pipelined with
double-precision inputs, the previous multiplier operation is advanced to the second
stage and a single- or double-precision zero is placed in the last stage of the pipeline.
The next pipelined multiplier operation stores zero instead of the result of the prior
operation, and the MRP bit of
fsr
for that next operation is undefined.
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