From: Jacob Lifshay <programmerjake@gmail.com>
Date: Mon, 18 Apr 2022 17:07:36 +0000 (-0700)
Subject: revert to original code from hackers delight
X-Git-Tag: opf_rfc_ls005_v1~2731
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=34a32aaf6daf9addcb3ba370d3c4db8e1ac29e9e;p=libreriscv.git

revert to original code from hackers delight

this reverts to the code from commit d23c78621366e1748bb6a782c08225e5faeac179
---

diff --git a/openpower/sv/bitmanip/divmnu64.c b/openpower/sv/bitmanip/divmnu64.c
index 52663f755..2bdb5bbbb 100644
--- a/openpower/sv/bitmanip/divmnu64.c
+++ b/openpower/sv/bitmanip/divmnu64.c
@@ -107,55 +107,14 @@ again:
 
       // Multiply and subtract.
       k = 0;
-#ifdef ORIGINAL
       for (i = 0; i < n; i++) {
          p = qhat*vn[i];
          t = un[i+j] - k - (p & 0xFFFFFFFFLL);
-         un[i+j] = (t & 0xffffffffLL);
+         un[i+j] = t;
          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+1; i++) {
-         unsigned rhi;
-         unsigned long long sum;
-         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
-#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
-      for (i = 0; i < n; i++) {
-        unsigned long long p = qhat*vn[i];
-        plo[i] = un[i+j] - (p&0xffffffffLL);
-        phi[i] = p >> 32;
-      }
-      for (i = 0; i < n; i++) {
-         t = plo[i] - k; // subtract previous carry
-         un[i+j] = (t & 0xffffffffLL);
-         k = phi[i] - (t >> 32); // take top-halves for new carry
-      }
-      t = un[j+n] - k;
-      un[j+n] = t;
-#endif
 
       q[j] = qhat;              // Store quotient digit.
       if (t < 0) {              // If we subtracted too