From: Luke Kenneth Casson Leighton <lkcl@lkcl.net>
Date: Mon, 18 Apr 2022 16:42:41 +0000 (+0100)
Subject: trying to get EXPERIMENT1 working
X-Git-Tag: opf_rfc_ls005_v1~2732
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=3fb634270f740460f35082544885127e29984cc4;p=libreriscv.git

trying to get EXPERIMENT1 working
---

diff --git a/openpower/sv/bitmanip/divmnu64.c b/openpower/sv/bitmanip/divmnu64.c
index 192fa1674..52663f755 100644
--- a/openpower/sv/bitmanip/divmnu64.c
+++ b/openpower/sv/bitmanip/divmnu64.c
@@ -114,20 +114,32 @@ again:
          un[i+j] = (t & 0xffffffffLL);
          k = (p >> 32) - (t >> 32);
       }
+      t = un[j+n] - k;
+      un[j+n] = t;
 #endif
+#define EXPERIMENT1
+      k = 1;
 #ifdef EXPERIMENT1
-      for (i = 0; i < n; i++) {
+      for (i = 0; i < n+1; i++) {
          unsigned rhi;
          unsigned long long sum;
-         p = ((unsigned long long)un[i+j])+ ~(qhat*vn[i]) + k;
-         rhi = (p >> 32);
+         if (i != n) {
+             p = qhat*vn[i];
+             sum = ((unsigned long long)un[i+j]) + ~p + k;
+         } else { // for last loop instead of separate cleanup do special sum
+            sum = (~0)+k;
+         }
+         rhi = (sum >> 32);
          if (((unsigned long long)k) <= 1) rhi += 1;
          k = rhi;
          un[i+j] = sum & 0xffffffff;
       }
+      // XXX t is not properly computed, it must contain -ve
+      // if the subtract should not have occurred
 #endif
-#define EXPERIMENT2
+//#define EXPERIMENT2
 #ifdef EXPERIMENT2
+      k = 0;
       unsigned long phi[200]; // yes, not malloced, we know
       unsigned long plo[200]; // yes, not malloced, we know
       // double-width multiply with strange subtract only on bottom half
@@ -141,9 +153,9 @@ again:
          un[i+j] = (t & 0xffffffffLL);
          k = phi[i] - (t >> 32); // take top-halves for new carry
       }
-#endif
       t = un[j+n] - k;
       un[j+n] = t;
+#endif
 
       q[j] = qhat;              // Store quotient digit.
       if (t < 0) {              // If we subtracted too