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[libreriscv.git] / simple_v_extension / daxpy_example.mdwn

diff --git a/simple_v_extension/daxpy_example.mdwn b/simple_v_extension/daxpy_example.mdwn
index 4e3163242541ad11c38361acba059123d445ca5a..5acea7e9fa14fdbf44f5e8375dcccab8e310c594 100644 (file)
--- a/simple_v_extension/daxpy_example.mdwn
+++ b/simple_v_extension/daxpy_example.mdwn
@@ -1,36 +1,48 @@
 # c code
 
 ```
-    void daxpy(size_t n, double a, const double x[], double y[])
-    {
-     for (size_t i = 0; i < n; i++) {
-       y[i] = a*x[i] + y[i];
-     }
+    void daxpy(size_t n, double a, const double x[], double y[]) {
+        for (size_t i = 0; i < n; i++)
+            y[i] = a*x[i] + y[i];
     }
 ```
 
+Summary
+
+| ISA | total | loop | words | notes |
+|-----|-------|------|-------|-------|
+| SVP64 | 9 | 7 | 14 | 5 64-bit, 4 32-bit |
+| RVV | 13 | 11 | 9.5 | 7 32-bit, 5 16-bit |
+| SVE | 12 | 7 | 12 | all 32-bit |
+
 # SVP64 Power ISA version
 
-```  
+Relies on post-increment, relies on no overlap between x and y
+in memory, and critically relies on y overwrite. x is post-incremented
+when read, but y is post-incremented on write. Element-Strided
+ensures the Immediate (8) results in a contiguous LD (or store)
+despite RA being marked Scalar (*without* modifying RA, on `sv.lfd/els`).
+For `sv.lfdup`, RA is Scalar so that only one
+LD/ST Update "wins": the last write to RA is the address for
+the next block.
 
-    # r5: n count
-    # r6: x ptr
-    # r7: y ptr
-    # fp1: a mul-scalar
-    mtctr 5                # move n to CTR
-    addi r10,r6,0          # copy y-ptr into r10
-.L2
-    setvl MAXVL=32,VL=CTR  # could do more
-    sv.lfdup/els *32,8(6)  # load from x into fp32-63
-    sv.lfdup/els *64,8(7)  # load from y into fp64-95
-    sv.fmadd *64,*64,1,*32 # (*y) = (*y) * (*x) + fp1
-    stfdup/els *64,8(10)   # store y-copy
-    sv.bc/ctr .L2          # decrement VL by CTR
-    blr                    # return
+```
+    # r5: n count; r6: x ptr; r7: y ptr; fp1: a
+    1  addi r3,r7,0           # return result
+    2  mtctr 5                # move n to CTR
+    3  .L2
+    4  setvl MAXVL=32,VL=CTR  # actually VL=MIN(MAXVL,CTR)
+    5  sv.lfdup/els *32,8(6)  # load x into fp32-63, incr x
+    6  sv.lfd/els *64,8(7)    # load y into fp64-95, NO INC
+    7  sv.fmadd *64,*64,1,*32 # (*y) = (*y) * (*x) + a
+    8  sv.stfdup/els *64,8(7) # store at y, incr y
+    9  sv.bc/ctr .L2          # decr CTR by VL, jump !zero
+    10 blr                    # return
 ```
 
 # RVV version
 
+
 ```
     # a0 is n, a1 is pointer to x[0], a2 is pointer to y[0], fa0 is a
       li t0, 2<<25