patch 8.2.5004: right shift on negative number does not work as documented

Problem:    Right shift on negative number does not work as documented.
Solution:   Use a uvarnumber_T type cast.

diff --git a/runtime/doc/eval.txt b/runtime/doc/eval.txt
index f9443fd297e4546633cb02490464ecf6258a2afa..77822d7963602092aa6dfd90b8b08059e6e678d7 100644 (file)
--- a/runtime/doc/eval.txt
+++ b/runtime/doc/eval.txt
@@ -1138,9 +1138,10 @@ expr6 >> expr6   bitwise right shift                             *expr->>*
                                                        *E1282* *E1283*
 The "<<" and ">>" operators can be used to perform bitwise left or right shift
 of the left operand by the number of bits specified by the right operand.  The
-operands must be positive numbers.  The topmost bit (sign bit) is always
-cleared for ">>".  If the right operand (shift amount) is more than the
-maximum number of bits in a number (|v:numbersize|) the result is zero.
+operands are used as positive numbers.  When shifting right with ">>" the
+topmost bit (somtimes called the sign bit) is cleared.  If the right operand
+(shift amount) is more than the maximum number of bits in a number
+(|v:numbersize|) the result is zero.
 
 
 expr6 and expr7                                *expr6* *expr7* *E1036* *E1051*
@@ -1417,6 +1418,10 @@ number                   number constant                 *expr-number*
 Decimal, Hexadecimal (starting with 0x or 0X), Binary (starting with 0b or 0B)
 and Octal (starting with 0, 0o or 0O).
 
+Assuming 64 bit numbers are used (see |v:numbersize|) an unsigned number is
+truncated to 0x7fffffffffffffff or 9223372036854775807.  You can use -1 to get
+0xffffffffffffffff.
+
                                                *floating-point-format*
 Floating point numbers can be written in two forms:
 

diff --git a/src/charset.c b/src/charset.c
index 34751e1862e4c208b20cb6537ee4f0c51ac3fbba..203a8fe0f9456fad228ce38357ee5df57dff5d71 100644 (file)
--- a/src/charset.c
+++ b/src/charset.c
@@ -2002,6 +2002,7 @@ vim_str2nr(
        }
        else
        {
+           // prevent a larg unsigned number to become negative
            if (un > VARNUM_MAX)
                un = VARNUM_MAX;
            *nptr = (varnumber_T)un;

diff --git a/src/eval.c b/src/eval.c
index 0ac2dfb35830bf670f68758e9a673e7f487ac2f1..7f90954667b190284268e7a1c65a64d8094b2a8c 100644 (file)
--- a/src/eval.c
+++ b/src/eval.c
@@ -3091,12 +3091,8 @@ eval5(char_u **arg, typval_T *rettv, evalarg_T *evalarg)
                rettv->vval.v_number =
                                    rettv->vval.v_number << var2.vval.v_number;
            else
-           {
                rettv->vval.v_number =
-                                   rettv->vval.v_number >> var2.vval.v_number;
-               // clear the topmost sign bit
-               rettv->vval.v_number &= ~((uvarnumber_T)1 << MAX_LSHIFT_BITS);
-           }
+                     (uvarnumber_T)rettv->vval.v_number >> var2.vval.v_number;
        }
 
        clear_tv(&var2);

diff --git a/src/testdir/test_expr.vim b/src/testdir/test_expr.vim
index 24daeb6655b6f84eb70cc2da9fd47eacef026720..ffac6df8064aacd62b798437b1caf21642d62792 100644 (file)
--- a/src/testdir/test_expr.vim
+++ b/src/testdir/test_expr.vim
@@ -958,6 +958,8 @@ func Test_bitwise_shift()
     call assert_equal(0, 0 >> 4)
     call assert_equal(0, 999999 >> 100)
     call assert_equal(0, 999999 << 100)
+    call assert_equal(-1, -1 >> 0)
+    call assert_equal(-1, -1 << 0)
     VAR a = 8
     VAR b = 2
     call assert_equal(2, a >> b)
@@ -976,6 +978,15 @@ func Test_bitwise_shift()
     for i in range(0, v:numbersize - 2)
         LET val = and(val, invert(1 << i))
     endfor
+    #" -1 has all the bits set
+    call assert_equal(-2, -1 << 1)
+    call assert_equal(-4, -1 << 2)
+    call assert_equal(-8, -1 << 3)
+    if v:numbersize == 64
+      call assert_equal(0x7fffffffffffffff, -1 >> 1)
+      call assert_equal(0x3fffffffffffffff, -1 >> 2)
+      call assert_equal(0x1fffffffffffffff, -1 >> 3)
+    endif
     call assert_equal(0, val)
     #" multiple operators
     call assert_equal(16, 1 << 2 << 2)

diff --git a/src/version.c b/src/version.c
index a6570a3cf2f417b5addc9b7e89467913a8b90bb7..e8799ad5765a236dc93bfe8d061303aa77bd5e67 100644 (file)
--- a/src/version.c
+++ b/src/version.c
@@ -734,6 +734,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    5004,
 /**/
     5003,
 /**/

diff --git a/src/vim9execute.c b/src/vim9execute.c
index b4fd9d591bb252fd4a5664692ec2352c230d4968..5410aa28411a69e0d8b97e470418f61ddfc3739e 100644 (file)
--- a/src/vim9execute.c
+++ b/src/vim9execute.c
@@ -4096,12 +4096,7 @@ exec_instructions(ectx_T *ectx)
                        case EXPR_RSHIFT: if (arg2 > MAX_LSHIFT_BITS)
                                              res = 0;
                                          else
-                                         {
-                                             res = arg1 >> arg2;
-                                             // clear the topmost sign bit
-                                             res &= ~((uvarnumber_T)1
-                                                          << MAX_LSHIFT_BITS);
-                                         }
+                                             res = (uvarnumber_T)arg1 >> arg2;
                                          break;
                        default: break;
                    }

diff --git a/src/vim9expr.c b/src/vim9expr.c
index c84be874af3581d17ca83ec0e7bd64beb6b6193b..3e720d913558565e28b18bf963c8588d0d80e51d 100644 (file)
--- a/src/vim9expr.c
+++ b/src/vim9expr.c
@@ -2719,11 +2719,8 @@ compile_expr5(char_u **arg, cctx_T *cctx, ppconst_T *ppconst)
            else if (type == EXPR_LSHIFT)
                tv1->vval.v_number = tv1->vval.v_number << tv2->vval.v_number;
            else
-           {
-               tv1->vval.v_number = tv1->vval.v_number >> tv2->vval.v_number;
-               // clear the topmost sign bit
-               tv1->vval.v_number &= ~((uvarnumber_T)1 << MAX_LSHIFT_BITS);
-           }
+               tv1->vval.v_number =
+                       (uvarnumber_T)tv1->vval.v_number >> tv2->vval.v_number;
            clear_tv(tv2);
            --ppconst->pp_used;
        }