Floating-Point Tag Word; Floating-Point Status Word - Intel Quark SoC X1000 Core Developer's Manual

4.5.2

Floating-Point Tag Word

The tag word marks the content of each numeric data register, as shown in
Each two-bit tag represents one of the eight data registers. The principal function of
the tag word is to optimize the FPU's performance and stack handling by making it
possible to distinguish between empty and non-empty register locations. It also
enables exception handlers to check the contents of a stack location without the need
to perform complex decoding of the actual data.
Figure 16.

Floating-Point Tag Word

15
Tag (7)
Note:
The index i of tag(i) is not top-relative. A program typically uses the "top" field of Status Word to
determine which tag(i) field refers to logical top of stack.
Tag Values:
00 = Valid
01 = Zero
10 = QNaN, SNaN, Infinity, Denormal, and Unsupported Formats
11 = Empty
4.5.3

Floating-Point Status Word

The 16-bit status word reflects the overall state of the FPU. The status word is shown in
Figure 17
®
Intel Quark SoC X1000 Core
Developer's Manual
54
Tag (6) Tag (5) Tag (4)
and is located in the status register.
®
Intel Quark Core—System Register Organization
Tag (3) Tag (2) Tag (1)
Figure 16.
0
Tag (0)
A5151-01
October 2013
Order Number: 329679-001US