19 Load Floating-point Immediate

The Zfa extension introduces fli.\{h|s|d|q\} instructions for loading a specific set of floating-point immediates, supported values can be found in the RISC-V ISA specification but are also listed below.

The fli instruction is used to load a floating point immediate into a floating register, the accepted immediate is defined in Floating-point literals and the reference table can be found in FLI operands reference table.

  fli.s fa0, 0x1p-15
  fli.s fa1, 0.00390625
  fli.s fa2, 6.25e-02

The tool should reject any value that does not exactly match a floating-point immediate operand for the 'fli' instruction.

RISC-V does not offer a generic pseudoinstruction to load an arbitrary floating point immediate value. Instead, a programmer can use the .float/.double directive to declare a floating point immediate value in the source code, and then load it into a floating point register using the load global pseudoinstruction (fl\{h|w|d|q\}).

  .data
.VAL:
  .float .0x1p+17
  .text
  flw fa0, .VAL, t0

Table 4. FLI operands reference table

| Value | Example legal input values | | -1.0 | -0x1p+0, -1.0, -1.0e+0 | | Minimum positive normal | min | | 1.0 x 2 ^ -16 | 0x1p-16, 0.0000152587890625, 1.52587890625e-05 | | 1.0 x 2 ^ -15 | 0x1p-15, 0.000030517578125, 3.0517578125e-05 | | 1.0 x 2 ^ -8 | 0x1p-8, 0.00390625, 3.90625e-03 | | 1.0 x 2 ^ -7 | 0x1p-7, 0.0078125, 7.8125e-03 | | 0.0625 (2 ^ -4) | 0x1p-4, 0.0625, 6.25e-02 | | 0.125 (2 ^ -3) | 0x1p-3, 0.125, 1.25e-01 | | 0.25 | 0x1p-2, 0.25, 2.5e-01 | | 0.3125 | 0x1.4p-2, 0.3125, 3.125e-01 | | 0.375 | 0x1.8p-2, 0.375, 3.75e-01 | | 0.4375 | 0x1.cp-2, 0.4375, 4.375e-01 | | 0.5 | 0x1p-1, 0.5, 5.0e-01 | | 0.625 | 0x1.4p-1, 0.625, 6.25e-01 | | 0.75 | 0x1.8p-1, 0.75, 7.5e-01 | | 0.875 | 0x1.cp-1, 0.875, 8.75e-01 | | 1.0 | 0x1p+0, 1.0, 1.0e+00 | | 1.25 | 0x1.4p+0, 1.25, 1.25e+00 | | 1.5 | 0x1.8p+0, 1.5, 1.5e+00 | | 1.75 | 0x1.cp+0, 1.75, 1.75e+00 | | 2.0 | 0x1p+1, 2.0, 2.0e+00 | | 2.5 | 0x1.4p+1, 2.5, 2.5e+00 | | 3 | 0x1.8p+1, 3.0, 3.0e+00 | | 4 | 0x1p+2, 4.0, 4.0e+00 | | 8 | 0x1p+3, 8.0, 8.0e+00 | | 16 | 0x1p+4, 16.0, 1.6e+01 | | 128 (2 ^ 7) | 0x1p+7, 128.0, 1.28e+02 | | 256 (2 ^ 8) | 0x1p+8, 256.0, 2.56e+02 | | 2 ^ 15 | 0x1p+15, 32768.0, 3.2768e+04 | | 2 ^ 16 | 0x1p+16, 65536.0, 6.5536e+04 | | Positive infinity | inf | | Canonical NaN | nan |

A value can be expressed in various forms within the same format. For example, 6.5536e+04 can be alternatively written as 6553.6e+01 or 65.536e+03. The table provides one possible representation, but any equivalent exact value may be used.