simple_v_extension/daxpy_example.mdwn

   1     # c code
   2     void daxpy(size_t n, double a, const double x[], double y[])
   3     {
   4      for (size_t i = 0; i < n; i++) {
   5        y[i] = a*x[i] + y[i];
   6      }
   7     }
   8
   9     # SV Version
  10     # a0 is n, a1 is ptr to x[0], a2 is ptr to y[0], fa0 is a (scalar)
  11       VBLK.REG[0] = {type: F, isvec: 1, regkey: a3, regidx: a3, elwidth: dflt}
  12       VBLK.REG[1] = {type: F, isvec: 1, regkey: a7, regidx: a7, elwidth: dflt}
  13     loop:
  14       VBLK.SETVL  t0, a0, #4   # MVL=4, vl = t0 = min(a0, MVL))
  15       c.ld     a3, a1          # load 4 registers a3-6 from x
  16       c.slli   t1, t0, 3       # t1 = vl * 8 (in bytes: FP is double)
  17       c.ld     a7, a2          # load 4 registers a7-10 from y
  18       c.add    a1, a1, t1      # increment pointer to x by vl*8
  19       fmadd  a7, a3, fa0, a7   # v1 += v0 * fa0 (y = a * x + y)
  20       c.sub    a0, a0, t0      # n -= vl (t0)
  21       c.st     a7, a2          # store 4 registers a7-10 to y
  22       c.add    a2, a2, t1      # increment pointer to y by vl*8
  23       c.bnez   a0, loop        # repeat if n != 0
  24       c.ret                    # return
  25
  26     # RVV version
  27     # a0 is n, a1 is pointer to x[0], a2 is pointer to y[0], fa0 is a
  28       li t0, 2<<25
  29       vsetdcfg t0             # enable 2 64b Fl.Pt. registers
  30     loop:
  31       setvl  t0, a0           # vl = t0 = min(mvl, n)
  32       vld    v0, a1           # load vector x
  33       c.slli   t1, t0, 3      # t1 = vl * 8 (in bytes)
  34       vld    v1, a2           # load vector y
  35       c.add    a1, a1, t1     # increment pointer to x by vl*8
  36       vfmadd v1, v0, fa0, v1  # v1 += v0 * fa0 (y = a * x + y)
  37       c.sub    a0, a0, t0     # n -= vl (t0)
  38       vst    v1, a2           # store Y
  39       c.add    a2, a2, t1     # increment pointer to y by vl*8
  40       c.bnez   a0, loop       # repeat if n != 0
  41       c.ret                   # return