Backport #33318. nv_overflows_integers_at

p4raw-id: //depot/metaconfig@33319

diff --git a/U/perl/perlxv.U b/U/perl/perlxv.U
index 8f1d272..5d00582 100644 (file)
--- a/U/perl/perlxv.U
+++ b/U/perl/perlxv.U
@@ -6,9 +6,10 @@
 ?RCS: License or the Artistic License, as specified in the README file.
 ?RCS:
 ?MAKE:ivtype uvtype nvtype ivsize uvsize nvsize \
-       i8type u8type i16type u16type i32type u32type i64type u64type \
-       i8size u8size i16size u16size i32size u32size i64size u64size \
-       d_nv_preserves_uv nv_preserves_uv_bits d_nv_zero_is_allbits_zero: \
+      i8type u8type i16type u16type i32type u32type i64type u64type \
+      i8size u8size i16size u16size i32size u32size i64size u64size \
+      d_nv_preserves_uv nv_preserves_uv_bits nv_overflows_integers_at \
+      d_nv_zero_is_allbits_zero: \
        echo rm_try use64bitint d_quad quadtype uquadtype \
        d_longdbl uselongdouble longdblsize doublesize \
        shortsize intsize longsize i_stdlib i_string \
@@ -88,6 +89,11 @@
 ?S:    This variable indicates how many of bits type uvtype
 ?S:    a variable nvtype can preserve.
 ?S:.
+?S:nv_overflows_integers_at:
+?S:    This variable gives the largest integer value that NVs can hold
+?S:    as a constant floating point expression.
+?S:    If it could not be determined, it holds the value 0.
+?S:.
 ?S:d_nv_zero_is_allbits_zero:
 ?S:    This variable indicates whether a variable of type nvtype
 ?S:    stores 0.0 in memory as all bits zero.
@@ -166,6 +172,12 @@
 ?C:    This symbol contains the number of bits a variable of type NVTYPE
 ?C:    can preserve of a variable of type UVTYPE.
 ?C:.
+?C:NV_OVERFLOWS_INTEGERS_AT:
+?C:    This symbol gives the largest integer value that NVs can hold. This
+?C:    value + 1.0 cannot be stored accurately. It is expressed as constant
+?C:    floating point expression to reduce the chance of decimale/binary
+?C:    conversion issues. If it can not be determined, the value 0 is given.
+?C:.
 ?C:NV_ZERO_IS_ALLBITS_ZERO:
 ?C:    This symbol, if defined, indicates that a variable of type NVTYPE
 ?C:    stores 0.0 in memory as all bits zero.
@@ -198,6 +210,7 @@
 ?H:#define     NVSIZE          $nvsize         /**/
 ?H:#$d_nv_preserves_uv NV_PRESERVES_UV
 ?H:#define     NV_PRESERVES_UV_BITS    $nv_preserves_uv_bits
+?H:#define     NV_OVERFLOWS_INTEGERS_AT        $nv_overflows_integers_at
 ?H:#$d_nv_zero_is_allbits_zero NV_ZERO_IS_ALLBITS_ZERO
 ?H:?%<:#if UVSIZE == 8
 ?H:?%<:#   ifdef BYTEORDER
@@ -431,6 +444,89 @@ case "$nv_preserves_uv_bits" in
 esac
 $rm_try
 
+$echo "Checking to find the largest integer value your NVs can hold..." >&4
+: volatile so that the compiler has to store it out to memory.
+if test X"$d_volatile" = X"$define"; then
+       volatile=volatile
+fi
+$cat <<EOP >try.c
+#include <stdio.h>
+
+typedef $nvtype NV;
+
+int
+main() {
+  NV value = 2;
+  int count = 1;
+
+  while(count < 256) {
+    $volatile NV up = value + 1.0;
+    $volatile NV negated = -value;
+    $volatile NV down = negated - 1.0;
+    $volatile NV got_up = up - value;
+    int up_good = got_up == 1.0;
+    int got_down = down - negated;
+    int down_good = got_down == -1.0;
+
+    if (down_good != up_good) {
+      fprintf(stderr,
+             "Inconsistency - up %d %f; down %d %f; for 2**%d (%.20f)\n",
+             up_good, (double) got_up, down_good, (double) got_down,
+             count, (double) value);
+      return 1;
+    }
+    if (!up_good) {
+      while (1) {
+       if (count > 8) {
+         count -= 8;
+         fputs("256.0", stdout);
+       } else {
+         count--;
+         fputs("2.0", stdout);
+       }
+       if (!count) {
+         puts("");
+         return 0;
+       }
+       fputs("*", stdout);
+      }
+    }
+    value *= 2;
+    ++count;
+  }
+  fprintf(stderr, "Cannot overflow integer range, even at 2**%d (%.20f)\n",
+         count, (double) value);
+  return 1;
+}
+EOP
+set try
+
+nv_overflows_integers_at='0'
+if eval $compile; then
+    xxx="`$run ./try`"
+    case "$?" in
+       0)
+           case "$xxx" in
+               2*)  cat >&4 <<EOM
+The largest integer your NVs can preserve is equal to $xxx
+EOM
+                   nv_overflows_integers_at="$xxx"
+                   ;;
+               *)  cat >&4 <<EOM
+Cannot determine the largest integer value your NVs can hold, unexpected output
+'$xxx'
+EOM
+                   ;;
+           esac
+           ;;
+       *)  cat >&4 <<EOM
+Cannot determine the largest integer value your NVs can hold
+EOM
+           ;;
+    esac
+fi
+$rm_try
+
 $echo "Checking whether NV 0.0 is all bits zero in memory..." >&4
 : volatile so that the compiler has to store it out to memory.
 if test X"$d_volatile" = X"$define"; then