ztrans_proposal.mdwn

   1 # Ztrans - transcendental operations
   2
   3 See:
   4
   5 * <http://bugs.libre-riscv.org/show_bug.cgi?id=127>
   6 * <https://www.khronos.org/registry/spir-v/specs/unified1/OpenCL.ExtendedInstructionSet.100.html>
   7
   8 Extension subsets:
   9
  10 * **Ztrans**: standard transcendentals (best suited to 3D)
  11 * **ZtransExt**: extra functions (useful, not generally needed for 3D)
  12 * **Ztrigpi**: trig. xxx-pi sinpi cospi tanpi
  13 * **Ztrignpi**: trig non-xxx-pi sin cos tan
  14 * **Zarctrigpi**: arc-trig. a-xxx-pi: atan2pi asinpi acospi
  15 * **Zarctrignpi**: arc-trig. non-a-xxx-pi: atan2, asin, acos
  16 * **Ztrignh**: trig/arc-trig hyperbolic.  sinh cosh tanh, asinh, acosh, atanh
  17 * **ZtransAdv**: much more complex to implement in hardware
  18
  19 Minimum recommended requirements for 3D: Ztrans, Ztrigpi, Zarctrigpi,
  20 Zarctrignpi
  21
  22 [[!toc levels=2]]
  23
  24 # List of 2-arg opcodes
  25
  26 [[!table  data="""
  27 opcode    | Description           | pseudo-code                | Extension |
  28 FATAN2    | atan2 arc tangent     | rd = atan2(rs2, rs1)       | Zarctrignpi |
  29 FATAN2PI  | atan arc tangent / pi | rd = atan2(rs2, rs1) / pi  | Zarctrigpi |
  30 FPOW      | x power of y          | rd = pow(rs1, rs2)         | ZtransAdv |
  31 FROOT     | x power 1/y           | rd = pow(rs1, 1/rs2)       | ZtransAdv |
  32 """]]
  33
  34 # List of 1-arg transcendental opcodes
  35
  36 [[!table  data="""
  37 opcode   | Description              | pseudo-code             | Extension |
  38 FCBRT    | Cube Root                | rd = pow(rs1, 3)        | Ztrans    |
  39 FEXP2    | power-of-2               | rd = pow(2, rs1)        | Ztrans    |
  40 FLOG2    | log2                     | rd = log2(rs1)          | Ztrans    |
  41 FEXPM1   | exponent minus 1         | rd = pow(e, rs1) - 1.0  | Ztrans    |
  42 FLOG1P   | log plus 1               | rd = log(e, 1 + rs1)    | Ztrans    |
  43 FEXP     | exponent                 | rd = pow(e, rs1)        | ZtransExt |
  44 FLOG     | natural log (base e)     | rd = log(e, rs1)        | ZtransExt |
  45 FEXP10   | power-of-10              | rd = pow(10, rs1)       | ZtransExt |
  46 FLOG10   | log base 10              | rd = log10(rs1)         | ZtransExt |
  47 """]]
  48
  49 # List of 1-arg trigonometric opcodes
  50
  51 [[!table  data="""
  52 opcode   | Description              | pseudo-code             | Extension |
  53 FSIN     | sin (radians)            | rd = sin(rs1)           | Ztrignpi    |
  54 FCOS     | cos (radians)            | rd = cos(rs1)           | Ztrignpi    |
  55 FTAN     | tan (radians)            | rd = tan(rs1)           | Ztrignpi    |
  56 FASIN    | arcsin (radians)         | rd = asin(rs1)          | Zarctrignpi |
  57 FACOS    | arccos (radians)         | rd = acos(rs1)          | Zarctrignpi |
  58 FSINPI   | sin times pi             | rd = sin(pi * rs1)      | Ztrigpi |
  59 FCOSPI   | cos times pi             | rd = cos(pi * rs1)      | Ztrigpi |
  60 FTANPI   | tan times pi             | rd = tan(pi * rs1)      | Ztrigpi |
  61 FASINPI  | arcsin times pi          | rd = asin(pi * rs1)     | Zarctrigpi |
  62 FACOSPI  | arccos times pi          | rd = acos(pi * rs1)     | Zarctrigpi |
  63 FATANPI  | arctan times pi          | rd = atan(pi * rs1)     | Zarctrigpi |
  64 FSINH    | hyperbolic sin (radians) | rd = sinh(rs1)          | Ztrigh |
  65 FCOSH    | hyperbolic cos (radians) | rd = cosh(rs1)          | Ztrigh |
  66 FTANH    | hyperbolic tan (radians) | rd = tanh(rs1)          | Ztrigh |
  67 FASINH   | inverse hyperbolic sin   | rd = asinh(rs1)         | Ztrigh |
  68 FACOSH   | inverse hyperbolic cos   | rd = acosh(rs1)         | Ztrigh |
  69 FATANH   | inverse hyperbolic tan   | rd = atanh(rs1)         | Ztrigh |
  70 """]]
  71
  72 # Pseudo-code ops and macro-ops
  73
  74 The pseudo-ops are best left up to the compiler rather than being actual
  75 pseudo-ops, by allocating one scalar FP register for use as a constant
  76 (loop invariant) set to "1.0" at the beginning of a function or other
  77 suitable code block.
  78
  79 * FRCP rd, rs1 - pseudo-code alias for rd = 1.0 / rs1
  80 * FATAN - pseudo-code alias for rd = atan2(rs1, 1.0) - FATAN2
  81 * FATANPI - pseudo alias for rd = atan2pi(rs1, 1.0) - FATAN2PI
  82 * FSINCOS - fused macro-op between FSIN and FCOS (issued in that order).
  83 * FSINCOSPI - fused macro-op between FSINPI and FCOSPI (issued in that order).
  84
  85 FATANPI example pseudo-code:
  86
  87     lui t0, 0x3F800 // upper bits of f32 1.0
  88     fmv.x.s ft0, t0
  89     fatan2pi.s rd, rs1, ft0
  90