**Target**: v3.2B
-**Source**: v3.0B
+**Source**: v3.1B
**Books and Section affected**:
**Keywords**:
```
- GPR, FPR, minmax
+ GPR, FPR, min, max, fmin, fmax
```
**Motivation**
**Notes and Observations**:
-1. TODO
+1. minimum/maximum instructions are needed for vector reductions, where the SVP64 tree reduction needs a single instruction to work properly.
+2. if you implement any of the FP min/max modes, the rest are not much more hardware.
+3. FP min/max are rather complex to implement in software, the most commonly used FP max function `fmax` from glibc compiled for SFFS is 32 (!) instructions.
+
+https://gcc.godbolt.org/z/6xba61To6
+
+```
+ fmax(double, double):
+ fcmpu 0,1,2
+ fmr 0,1
+ cror 30,1,2
+ beq 7,.L12
+ blt 0,.L13
+ stfd 1,-16(1)
+ lis 9,0x8
+ li 8,-1
+ sldi 9,9,32
+ rldicr 8,8,0,11
+ ori 2,2,0
+ ld 10,-16(1)
+ xor 10,10,9
+ sldi 10,10,1
+ cmpld 0,10,8
+ bgt 0,.L5
+ stfd 2,-16(1)
+ ori 2,2,0
+ ld 10,-16(1)
+ xor 9,10,9
+ sldi 9,9,1
+ cmpld 0,9,8
+ ble 0,.L6
+.L5:
+ fadd 1,0,2
+ blr
+.L13:
+ fmr 1,2
+ blr
+.L6:
+ fcmpu 0,2,2
+ fmr 1,2
+ bnulr 0
+.L12:
+ fmr 1,0
+ blr
+ .long 0
+ .byte 0,9,0,0,0,0,0,0
+```
**Changes**
Add the following entries to:
* the Appendices of Book I
-* Instructions of Book I added to Section 3.3.14.2
+* Book I 3.3.9 Fixed-Point Arithmetic Instructions
+* Book I 4.6.6.1 Floating-Point Elementary Arithmetic Instructions
+* Book I 1.6.1 and 1.6.2
----------------
\newpage{}
+## `FMM` -- Floating Min/Max Mode
+
+<a id="fmm-floating-min-max-mode"></a>
+
+| `FMM` | Assembly Alias | Origin | Semantics |
+|-------|-------------------------------|--------------------------------|-------------------------------------------------|
+| 0000 | fminnum08[s] FRT, FRA, FRB | IEEE 754-2008 | FRT = minNum(FRA, FRB) (1) |
+| 0001 | fmin19[s] FRT, FRA, FRB | IEEE 754-2019 | FRT = minimum(FRA, FRB) |
+| 0010 | fminnum19[s] FRT, FRA, FRB | IEEE 754-2019 | FRT = minimumNumber(FRA, FRB) |
+| 0011 | fminc[s] FRT, FRA, FRB | x86 minss or Win32's min macro | FRT = FRA \< FRB ? FRA : FRB |
+| 0100 | fminmagnum08[s] FRT, FRA, FRB | IEEE 754-2008 (TODO: (3)) | FRT = minmaxmag(FRA, FRB, False, fminnum08) (2) |
+| 0101 | fminmag19[s] FRT, FRA, FRB | IEEE 754-2019 | FRT = minmaxmag(FRA, FRB, False, fmin19) (2) |
+| 0110 | fminmagnum19[s] FRT, FRA, FRB | IEEE 754-2019 | FRT = minmaxmag(FRA, FRB, False, fminnum19) (2) |
+| 0111 | fminmagc[s] FRT, FRA, FRB | - | FRT = minmaxmag(FRA, FRB, False, fminc) (2) |
+| 1000 | fmaxnum08[s] FRT, FRA, FRB | IEEE 754-2008 | FRT = maxNum(FRA, FRB) (1) |
+| 1001 | fmax19[s] FRT, FRA, FRB | IEEE 754-2019 | FRT = maximum(FRA, FRB) |
+| 1010 | fmaxnum19[s] FRT, FRA, FRB | IEEE 754-2019 | FRT = maximumNumber(FRA, FRB) |
+| 1011 | fmaxc[s] FRT, FRA, FRB | x86 maxss or Win32's max macro | FRT = FRA > FRB ? FRA : FRB |
+| 1100 | fmaxmagnum08[s] FRT, FRA, FRB | IEEE 754-2008 (TODO: (3)) | FRT = minmaxmag(FRA, FRB, True, fmaxnum08) (2) |
+| 1101 | fmaxmag19[s] FRT, FRA, FRB | IEEE 754-2019 | FRT = minmaxmag(FRA, FRB, True, fmax19) (2) |
+| 1110 | fmaxmagnum19[s] FRT, FRA, FRB | IEEE 754-2019 | FRT = minmaxmag(FRA, FRB, True, fmaxnum19) (2) |
+| 1111 | fmaxmagc[s] FRT, FRA, FRB | - | FRT = minmaxmag(FRA, FRB, True, fmaxc) (2) |
+
+Note (1): for the purposes of minNum/maxNum, -0.0 is defined to be less than +0.0. This is left unspecified in IEEE 754-2008.
+
+Note (2): minmaxmag(x, y, cmp, fallback) is defined as:
+
+```python
+def minmaxmag(x, y, is_max, fallback):
+ a = abs(x) < abs(y)
+ b = abs(x) > abs(y)
+ if is_max:
+ a, b = b, a # swap
+ if a:
+ return x
+ if b:
+ return y
+ # equal magnitudes, or NaN input(s)
+ return fallback(x, y)
+```
+
+Note (3): TODO: icr if IEEE 754-2008 has min/maxMagNum like IEEE 754-2019's minimum/maximumMagnitudeNumber
+
+----------------
+
+\newpage{}
+
+## Floating Minimum/Maximum X-Form
+
+```
+ fminmax FRT, FRA, FRB, FMM
+```
+
+```
+ |0 |6 |11 |16 |21 |24 |31 |
+ | PO | FRT | FRA | FRB | FMM[0:2] | XO | FMM[3] |
+```
+
+Compute the minimum/maximum of FRA and FRB, according to FMM, and store the result in FRT.
+
+Assembly Aliases: see [`FMM` -- Floating Min/Max Mode](#fmm-floating-min-max-mode)
+
+----------
+
+## Floating Minimum/Maximum Single X-Form
+
+```
+ fminmaxs FRT, FRA, FRB, FMM
+```
+
+```
+ |0 |6 |11 |16 |21 |24 |31 |
+ | PO | FRT | FRA | FRB | FMM[0:2] | XO | FMM[3] |
+```
+
+Compute the minimum/maximum of FRA and FRB, according to FMM, and store the result in FRT.
+
+Assembly Aliases: see [`FMM` -- Floating Min/Max Mode](#fmm-floating-min-max-mode)
+
+----------
+
+\newpage{}
+
+## Minimum Unsigned X-Form
+
+```
+ minu RT, RA, RB
+ minu. RT, RA, RB
+```
+
+```
+ |0 |6 |11 |16 |21 |31 |
+ | PO | RT | RA | RB | XO | Rc |
+```
+
+```
+ if (RA) <u (RB) then
+ RT <- (RA)
+ else
+ RT <- (RB)
+```
+
+Compute the unsigned minimum of RA and RB and store the result in RT.
+
+Special Registers altered:
+
+```
+ CR0 (if Rc=1)
+```
+
+----------
+
+## Maximum Unsigned X-Form
+
+```
+ maxu RT, RA, RB
+ maxu. RT, RA, RB
+```
+
+```
+ |0 |6 |11 |16 |21 |31 |
+ | PO | RT | RA | RB | XO | Rc |
+```
+
+```
+ if (RA) >u (RB) then
+ RT <- (RA)
+ else
+ RT <- (RB)
+```
+
+Compute the unsigned maximum of RA and RB and store the result in RT.
+
+Special Registers altered:
+
+```
+ CR0 (if Rc=1)
+```
+
+----------
+
+\newpage{}
+
+## Minimum X-Form
+
+```
+ min RT, RA, RB
+ min. RT, RA, RB
+```
+
+```
+ |0 |6 |11 |16 |21 |31 |
+ | PO | RT | RA | RB | XO | Rc |
+```
+
+```
+ if (RA) < (RB) then
+ RT <- (RA)
+ else
+ RT <- (RB)
+```
+
+Compute the signed minimum of RA and RB and store the result in RT.
+
+Special Registers altered:
+
+```
+ CR0 (if Rc=1)
+```
+
+----------
+
+## Maximum X-Form
+
+```
+ max RT, RA, RB
+ max. RT, RA, RB
+```
+
+```
+ |0 |6 |11 |16 |21 |31 |
+ | PO | RT | RA | RB | XO | Rc |
+```
+
+```
+ if (RA) > (RB) then
+ RT <- (RA)
+ else
+ RT <- (RB)
+```
+
+Compute the signed maximum of RA and RB and store the result in RT.
+
+Special Registers altered:
+
+```
+ CR0 (if Rc=1)
+```
+
+----------
+
+\newpage{}
+
+# Instruction Formats
+
+Add the following entries to Book I 1.6.1.15 X-FORM:
+
+```
+ |0 |6 |11 |16 |21 |24 |31 |
+ | PO | FRT | FRA | FRB | FMM[0:2] | XO | FMM[3] |
+```
+
+Add a new field to Book I 1.6.2 Word Instruction Fields:
+
+```
+ FMM (21:23,31)
+ Field used to specify minimum/maximum mode for fminmax[s].
+
+ Formats: X
+```
+
+----------
+
+\newpage{}
+
# Appendices
Appendix E Power ISA sorted by opcode
| Form | Book | Page | Version | mnemonic | Description |
|------|------|------|---------|----------|-------------|
-| Z23 | I | # | 3.0B | shadd | Shift-and-Add |
-| Z23 | I | # | 3.0B | shaddw | Shift-and-Add Signed Word |
-| Z23 | I | # | 3.0B | shadduw | Shift-and-Add Unsigned Word |
+| X | I | # | 3.2B | fminmax | Floating Minimum/Maximum |
+| X | I | # | 3.2B | fminmaxs | Floating Minimum/Maximum Single |
+| X | I | # | 3.2B | minu | Minimum Unsigned |
+| X | I | # | 3.2B | maxu | Maximum Unsigned |
+| X | I | # | 3.2B | min | Minimum |
+| X | I | # | 3.2B | max | Maximum |
[[!tag opf_rfc]]
projects / libreriscv.git / commitdiff