+**OBSOLETE**, superceded by [[openpower/transcendentals]]
+
# Summary FP Opcodes
This page aids and assists in the development of FP proposals,
Publicly-known FP proposals:
* Zfrsqrt - Reciprocal SQRT <http://bugs.libre-riscv.org/show_bug.cgi?id=110>
-* Zftrans - Transcendentals (FSIN, FCOS, FATAN, FPOW, FEXP, FLOG, FRCP)
+* Zftrans - see [[ztrans_proposal]]: Transcendentals
+ (FPOW, FEXP, FLOG, FCBRT)
<http://bugs.libre-riscv.org/show_bug.cgi?id=127>
+* Ztrig\* - see [[ztrans_proposal]]: Trigonometriics
+ (FSIN, FCOS, FTAN, arc-variants, hypotenuse-variants)
* Extension of formats to cover FP16 (RISC-V ISA Manual Table 11.3 "fmt field")
+ <https://groups.google.com/a/groups.riscv.org/d/msg/isa-dev/8knne5BtlvM>
* HI-half FP MV - <https://github.com/riscv/riscv-isa-manual/pull/301>
<https://groups.google.com/a/groups.riscv.org/forum/m/#!topic/isa-dev/kXgfFqgBv-c>
* (Add new entries here: Zextname - Description and URL)
* Both dual and single argument FP operations that do not require
"rounding mode" should go in one of the funct5 tables that already use
"funct3".
+* The rs2 field can be best used to sub-select a considerable number
+ of 1-op operations, with "rounding" in funct3
+* The funct3 field can be best used to sub-select a considerable number
+ of 2-op operations
+* 1-op operations that do not need "rounding" have the best brownfield
+ availability: 8 bit sub-selection (rs2=5 + funct3=3). This however is
+ rare as most FP operations need "rounding" selection.
* Be careful not to use encoding space for which FP16 has already been
- reserved.
+ reserved (mostly FP conversion opcodes)
[[!table data="""
-31..27 | 26..25 | 24..20 |19..15| 14...12| 11..7 | 6....0 | function |
-funct5 | SDHQ | rs2 | rs1 | funct3 | rd | opcode | name |
- 5 | 2 | 5 | 5 | 3 | 5 | 7 | |
-00000 | xx | rs2 | rs1 | rm | rd | 1010011 | FADD.xx |
-00001 | xx | rs2 | rs1 | rm | rd | 1010011 | FSUB.xx |
-00010 | xx | rs2 | rs1 | rm | rd | 1010011 | FMUL.xx |
-00011 | xx | rs2 | rs1 | rm | rd | 1010011 | FDIV.xx |
-00100 | xx | rs2 | rs1 | yyy | rd | 1010011 | ? |
-00101 | xx | rs2 | rs1 | yyy | rd | 1010011 | tb=00101 |
-00110 | xx | rs2 | rs1 | yyy | rd | 1010011 | ? |
-00111 | xx | rs2 | rs1 | yyy | rd | 1010011 | ? |
-01000 | xx | rs2 | rs1 | yyy | rd | 1010011 | tb=01000 |
-01001 | xx | rs2 | rs1 | yyy | rd | 1010011 | ? |
-01010 | xx | rs2 | rs1 | yyy | rd | 1010011 | ? |
-01011 | xx | xxxxx | rs1 | yyy | rd | 1010011 | tb=01011 |
-01100 | xx | rs2 | rs1 | yyy | rd | 1010011 | ? |
-01101 | xx | rs2 | rs1 | yyy | rd | 1010011 | ? |
-01110 | xx | rs2 | rs1 | yyy | rd | 1010011 | ? |
-01111 | xx | rs2 | rs1 | yyy | rd | 1010011 | **FPOW.xx** |
-10000 | xx | rs2 | rs1 | yyy | rd | 1010011 | ? |
-10001 | xx | rs2 | rs1 | yyy | rd | 1010011 | ? |
-10010 | xx | rs2 | rs1 | yyy | rd | 1010011 | ? |
-10011 | xx | rs2 | rs1 | yyy | rd | 1010011 | ? |
-10100 | xx | rs2 | rs1 | yyy | rd | 1010011 | tb=10100 |
-10101 | xx | rs2 | rs1 | yyy | rd | 1010011 | ? |
-10110 | xx | rs2 | rs1 | yyy | rd | 1010011 | ? |
-10111 | xx | rs2 | rs1 | yyy | rd | 1010011 | ? |
-11000 | xx | xxxxx | rs1 | yyy | rd | 1010011 | tb=11000 |
-11001 | xx | rs2 | rs1 | yyy | rd | 1010011 | ? |
-11010 | xx | xxxxx | rs1 | yyy | rd | 1010011 | tb=11010 |
-11100 | xx | xxxxx | rs1 | 000 | rd | 1010011 | tb=11100 |
-11101 | xx | rs2 | rs1 | yyy | rd | 1010011 | ? |
-11110 | xx | xxxxx | rs1 | 000 | rd | 1010011 | tb=11110 |
-11111 | xx | rs2 | rs1 | yyy | rd | 1010011 | ? |
+31..27 | 26..25 | 24..20 |19..15| 14...12| 11..7 | 6....0 | function |
+funct5 | SDHQ | rs2 | rs1 | funct3 | rd | opcode | name |
+ 5 | 2 | 5 | 5 | 3 | 5 | 7 | |
+00000 | xx | rs2 | rs1 | rm | rd | 1010011 | FADD.xx |
+00001 | xx | rs2 | rs1 | rm | rd | 1010011 | FSUB.xx |
+00010 | xx | rs2 | rs1 | rm | rd | 1010011 | FMUL.xx |
+00011 | xx | rs2 | rs1 | rm | rd | 1010011 | FDIV.xx |
+00100 | xx | rs2 | rs1 | yyy | rd | 1010011 | ? |
+00101 | xx | rs2 | rs1 | yyy | rd | 1010011 | tb=00101 |
+00110 | xx | rs2 | rs1 | yyy | rd | 1010011 | ? |
+00111 | xx | rs2 | rs1 | yyy | rd | 1010011 | ? |
+01000 | xx | rs2 | rs1 | yyy | rd | 1010011 | tb=01000 |
+01001 | xx | rs2 | rs1 | yyy | rd | 1010011 | ? |
+01010 | xx | rs2 | rs1 | yyy | rd | 1010011 | ? |
+01011 | xx | xxxxx | rs1 | yyy | rd | 1010011 | tb=01011 |
+01100 | xx | rs2 | rs1 | yyy | rd | 1010011 | **FHYPOT.xx** |
+01101 | xx | rs2 | rs1 | rm | rd | 1010011 | **FATAN2.xx** |
+01110 | xx | rs2 | rs1 | rm | rd | 1010011 | **FATAN2PI.xx**|
+01111 | xx | rs2 | rs1 | rm | rd | 1010011 | **FPOW.xx** |
+10000 | xx | rs2 | rs1 | yyy | rd | 1010011 | **FROOTN.xx** |
+10001 | xx | rs2 | rs1 | yyy | rd | 1010011 | **FPOWN.xx** |
+10010 | xx | rs2 | rs1 | yyy | rd | 1010011 | **FPOWR.xx** |
+10011 | xx | rs2 | rs1 | yyy | rd | 1010011 | ? |
+10100 | xx | rs2 | rs1 | yyy | rd | 1010011 | tb=10100 |
+10101 | xx | rs2 | rs1 | yyy | rd | 1010011 | ? |
+10110 | xx | rs2 | rs1 | yyy | rd | 1010011 | ? |
+10111 | xx | rs2 | rs1 | yyy | rd | 1010011 | ? |
+11000 | xx | xxxxx | rs1 | yyy | rd | 1010011 | tb=11000 |
+11001 | xx | rs2 | rs1 | yyy | rd | 1010011 | ? |
+11010 | xx | xxxxx | rs1 | yyy | rd | 1010011 | tb=11010 |
+11100 | xx | xxxxx | rs1 | yyy | rd | 1010011 | tb=11100 |
+11101 | xx | rs2 | rs1 | yyy | rd | 1010011 | ? |
+11110 | xx | xxxxx | rs1 | yyy | rd | 1010011 | tb=11110 |
+11111 | xx | rs2 | rs1 | yyy | rd | 1010011 | ? |
"""]]
+Code:
+
+* xx: Opcode format field "fmt" - Table 11.3
+* xxxxx: 5-bit selection field (usually 1-op selection)
+* yyy: funct3 selection field (usually 2-op selection)
+* rm: "rounding mode"
+
## funct5 = 00000 - FADD
No brownfield encodings available.
Brownfield encodings available.
-## funct5 = 00100
+## funct5 = 00100 - FSGN
This table uses funct3 for encoding 2-operand FP operations
00100 | xx | rs2 | rs1 | 111 | rd | 1010011 | ?f3=111 |
"""]]
-## funct5 = 00101
+## funct5 = 00101 - FMIN/MAX
This table uses funct3 for encoding 2-operand FP operations where the result
register is a **floating-point** value.
Brownfield encodings available.
-## funct5 = 01000
+## funct5 = 01000 - FCVT
This table uses rs2 for encoding 1-operand FP operations, using
funct3 to specify the "rounding" mode
5 | 2 | 5 | 5 | 3 | 5 | 7 | |
01011 | xx | 00000 | rs1 | rm | rd | 1010011 | FSQRT.xx |
01011 | xx | 00001 | rs1 | rm | rd | 1010011 | **FRSQRT.xx** |
-01011 | xx | 00010 | rs1 | rm | rd | 1010011 | **FRCP.xx** |
-01011 | xx | 00011 | rs1 | rm | rd | 1010011 | **CBRT.xx** |
-01011 | xx | 00100 | rs1 | rm | rd | 1010011 | ? |
-01011 | xx | 00101 | rs1 | rm | rd | 1010011 | ? |
-01011 | xx | 00110 | rs1 | rm | rd | 1010011 | ? |
-01011 | xx | 00111 | rs1 | rm | rd | 1010011 | ? |
-01011 | xx | 01000 | rs1 | rm | rd | 1010011 | **FEXP2.xx** |
-01011 | xx | 01001 | rs1 | rm | rd | 1010011 | **FLOG2.xx** |
-01011 | xx | 01010 | rs1 | rm | rd | 1010011 | **FEXPM1.xx** |
-01011 | xx | 01011 | rs1 | rm | rd | 1010011 | **FLOGP1.xx** |
-01011 | xx | 01100 | rs1 | rm | rd | 1010011 | **FEXP.xx** |
-01011 | xx | 01101 | rs1 | rm | rd | 1010011 | **FLOG.xx** |
-01011 | xx | 01110 | rs1 | rm | rd | 1010011 | **FEXP10.xx** |
-01011 | xx | 01111 | rs1 | rm | rd | 1010011 | **FLOG10.xx** |
+01011 | xx | 00010 | rs1 | rm | rd | 1010011 | **FRECIP.xx** |
+01011 | xx | 00011 | rs1 | rm | rd | 1010011 | **FCBRT.xx** |
+01011 | xx | 00100 | rs1 | rm | rd | 1010011 | **FEXP2.xx** |
+01011 | xx | 00101 | rs1 | rm | rd | 1010011 | **FLOG2.xx** |
+01011 | xx | 00110 | rs1 | rm | rd | 1010011 | **FEXPM1.xx** |
+01011 | xx | 00111 | rs1 | rm | rd | 1010011 | **FLOGP1.xx** |
+01011 | xx | 01000 | rs1 | rm | rd | 1010011 | **FEXP.xx** |
+01011 | xx | 01001 | rs1 | rm | rd | 1010011 | **FLOG.xx** |
+01011 | xx | 01010 | rs1 | rm | rd | 1010011 | **FEXP10.xx** |
+01011 | xx | 01011 | rs1 | rm | rd | 1010011 | **FLOG10.xx** |
+01011 | xx | 01100 | rs1 | rm | rd | 1010011 | **FASINH.xx** |
+01011 | xx | 01101 | rs1 | rm | rd | 1010011 | **FACOSH.xx** |
+01011 | xx | 01110 | rs1 | rm | rd | 1010011 | **FATANH.xx** |
+01011 | xx | 01111 | rs1 | rm | rd | 1010011 | ? |
01011 | xx | 10000 | rs1 | rm | rd | 1010011 | **FSIN.xx** |
-01011 | xx | 10001 | rs1 | rm | rd | 1010011 | **FCOS.xx** |
-01011 | xx | 10010 | rs1 | rm | rd | 1010011 | **FTAN.xx** |
-01011 | xx | 10011 | rs1 | rm | rd | 1010011 | **FTAN2.xx** |
-01011 | xx | 10100 | rs1 | rm | rd | 1010011 | **FSINPI.xx** |
-01011 | xx | 10101 | rs1 | rm | rd | 1010011 | **FCOSPI.xx** |
-01011 | xx | 10110 | rs1 | rm | rd | 1010011 | **FTANPI.xx** |
-01011 | xx | 10111 | rs1 | rm | rd | 1010011 | **FATAN2PI.xx**|
-01011 | xx | 11000 | rs1 | rm | rd | 1010011 | **FSINH.xx** |
-01011 | xx | 11001 | rs1 | rm | rd | 1010011 | **FCOSH.xx** |
-01011 | xx | 11010 | rs1 | rm | rd | 1010011 | **FTANH.xx** |
-01011 | xx | 11011 | rs1 | rm | rd | 1010011 | ? |
-01011 | xx | 11100 | rs1 | rm | rd | 1010011 | **FASINH.xx** |
-01011 | xx | 11101 | rs1 | rm | rd | 1010011 | **FACOSH.xx** |
-01011 | xx | 11110 | rs1 | rm | rd | 1010011 | **FATANH.xx** |
+01011 | xx | 10001 | rs1 | rm | rd | 1010011 | **FSINPI.xx** |
+01011 | xx | 10010 | rs1 | rm | rd | 1010011 | **FASIN.xx** |
+01011 | xx | 10011 | rs1 | rm | rd | 1010011 | **FASINPI.xx**|
+01011 | xx | 10100 | rs1 | rm | rd | 1010011 | **FCOS.xx** |
+01011 | xx | 10101 | rs1 | rm | rd | 1010011 | **FCOSPI.xx** |
+01011 | xx | 10110 | rs1 | rm | rd | 1010011 | **FACOS.xx** |
+01011 | xx | 10111 | rs1 | rm | rd | 1010011 | **FACOSPI.xx**|
+01011 | xx | 11000 | rs1 | rm | rd | 1010011 | **FTAN.xx** |
+01011 | xx | 11001 | rs1 | rm | rd | 1010011 | **FTANPI.xx** |
+01011 | xx | 11010 | rs1 | rm | rd | 1010011 | **FATAN.xx** |
+01011 | xx | 11011 | rs1 | rm | rd | 1010011 | **FATANPI.xx**|
+01011 | xx | 11100 | rs1 | rm | rd | 1010011 | **FSINH.xx** |
+01011 | xx | 11101 | rs1 | rm | rd | 1010011 | **FCOSH.xx** |
+01011 | xx | 11110 | rs1 | rm | rd | 1010011 | **FTANH.xx** |
01011 | xx | 11111 | rs1 | rm | rd | 1010011 | ? |
"""]]
-## funct5 = 01100 - unused
+## funct5 = 01100 - **FHYPOT**
-Brownfield encodings available.
+Proposed for Zftrans - FHYPOT: "sqrt(rs1 * rs1 + rs2 * rs2)"
-## funct5 = 01101 - unused
+## funct5 = 01101 - **FATAN2**
-Brownfield encodings available.
+Proposed for Zftrans - FATAN: "atan(rs1, rs2)"
-## funct5 = 01110 - unused
+## funct5 = 01110 - **FATAN2PI**
-Brownfield encodings available.
+Proposed for ZftransExt - FATAN2PI: "atan2(rs1, rs2) * PI".
+Rationale: Gives better accuracy than if using FMUL with the constant, PI.
## funct5 = 01111 - **FPOW**
-Proposed for Zftrans - FPOW: "FP rs2 to the power of rs1"
+Proposed for ZftransAdv - FPOW: "FP rs1 to the power of rs2"
-## funct5 = 10000 - unused
+## funct5 = 10000 - **FROOTN**
-Brownfield encodings available.
+Proposed for ZftransAdv - FPROOTN: "FP rs1 to the power of (1/rs2)".
+rs1 is FP, rs2 is **integer**.
-## funct5 = 10001 - unused
+## funct5 = 10000 - **FPOWN**
-Brownfield encodings available.
+Proposed for ZftransAdv - FPOW: "FP rs1 to the power of rs2"
+rs1 is FP, rs2 is **integer**.
+
+## funct5 = 10001 - **FPOW**
+
+Proposed for ZftransAdv - FPOWN: "FP rs1 to the power of rs2, rs1 +ve"
+rs1 and rs2 are FP, rs1 must be +ve. Equivalent to "exp(rs2 * log(rs1))"
## funct5 = 10010 - unused
Brownfield encodings available.
-## funct5 = 10100
+## funct5 = 10100 - FP comparisons
This table uses funct3 for encoding 2-operand FP "comparison" operations
where the result register is an **integer**
Brownfield encodings available.
-## funct5 = 11000
+## funct5 = 11000 - FCVT
This table uses rs2 for encoding 1-operand FP operations, using
funct3 to specify the "rounding" mode
Brownfield encodings available.
-## funct5 = 11010
+## funct5 = 11010 - FCVT
This table uses rs2 for encoding 1-operand FP operations, using
funct3 to specify the "rounding" mode
11010 | 11 | xxxxx | rs1 | rm | rd | 1010011 | rs2? |
"""]]
-## funct5 = 11100
+## funct5 = 11100 - FMV, FCLASS
This table uses *both* rs2 *and* funct3 for encoding 1-operand FP operations.
Brownfield encodings available.
-## funct5 = 11110
+## funct5 = 11110 - FMV
This table uses *both* rs2 *and* funct3 for encoding 1-operand FP operations.
projects / libreriscv.git / blobdiff