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floating-pointx86
Drathier
Drathier

Reputation: 14519

Do modern x86 processors have native support for decimal floating point arithmetic?

Do modern x86 processors have native support for decimal floating point arithmetic? I can't find anything about it online.

Upvotes: 8

Views: 1244

Answers (1)

user555045
user555045

Reputation: 64904

No, which may make it hard to find anything about it.

There are two instructions, fbld and fbstp, that deal with decimal floats, but they are just to convert from and to packed BCD representation. This is the only direct support for any decimal floating point, all arithmetic is on binary formats. These instructions are extremely microcoded, especially fbstp which often translates to 150-300 µops.

There are (or in some sense "have been") some integer instructions that would be useful when writing procedures that implement arithmetic on BCD floats (packed or unpacked), but they are obsolete and not supported in 64bit mode (and never constituted "native support for decimal floating point arithmetic" anyway). These are instructions such as aaa and daa.

Upvotes: 7

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