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Paul Mackerras
6fe4b549f5
There are two paths for multiply-add instructions; one where the product is larger or nearly the same as the addend, which does the addition/subtraction in the multiplier with 128-bit accuracy; the other is used when the addend is clearly larger, which shifts the product right before doing the addition/subtraction in 64-bit arithmetic. The threshold for the second path is that B_exp has to be greater than A_exp + C_exp + 1, the +1 being because the product mantissa can be greater than 2. This increases the +1 to +2 to make sure that the 128-bit path is used when there is any chance of cancellation of the high-order bits of the sum. With the +1 threshold we could still get close to cancellation when the mantissas of A and C were nearly 2 and the mantissa of B was 1. This improves accuracy and avoids the need to do a 120-bit subtraction in the second path. Signed-off-by: Paul Mackerras <paulus@ozlabs.org> |
1 week ago | |
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| Makefile | 5 years ago | |
| fpu.c | 1 week ago | |
| head.S | 5 years ago | |
| powerpc.lds | 5 years ago | |