frm

Floating-Point Dynamic Rounding Mode

Rounding modes are encoded as follows:

Table 1. Rounding mode encoding.
!Rounding Mode Mnemonic Meaning !000 !RNE !Round to Nearest, ties to Even !001 !RTZ !Round towards Zero !010 !RDN !Round Down (towards \(-\infty\)) !011 !RUP !Round Up (towards \(+\infty\)) !100 !RMM !Round to Nearest, ties to Max Magnitude !101 ! !Reserved for future use. !110 ! !Reserved for future use. !111 !DYN !In instruction’s rm field, selects dynamic rounding mode; In Rounding Mode register, reserved.

The behavior of floating-point instructions that depend on rounding mode when executed with a reserved rounding mode is reserved, including both static reserved rounding modes (101-110) and dynamic reserved rounding modes (101-111).

Some instructions, including widening conversions, have the rm field but are nevertheless mathematically unaffected by the rounding mode; software should set their rm field to RNE (000) but implementations must treat the rm field as usual (in particular, with regard to decoding legal vs. reserved encodings).

Attributes

CSR Address

0x2

Defining extension

  • F, version >= F@2.2.0

Length

32-bit

Privilege Mode

U

Format

frm format
Figure 1. frm format

Field Summary

Name Location Type Reset Value

ROUNDINGMODE

2:0

RW-H

UNDEFINED_LEGAL

Fields

ROUNDINGMODE

Location

frm[2:0]

Description

Rounding mode data.

Type

RW-H

Read-Write with Hardware update

Field is writable by software. Any value that fits in the field is acceptable. Hardware also updates the field without an explicit software write.
Reset value

UNDEFINED_LEGAL

Software write

This field has special behavior when written by software (e.g., through csrrw).

When software tries to write csr_value, the field will be written with the return value of the function below.

fcsr.FRM = csr_value.ROUNDINGMODE;
return csr_value.ROUNDINGMODE;

Software read

This CSR may return a value that is different from what is stored in hardware.

  • Pruned

  • Original

return fcsr.FRM;
return fcsr.FRM;