[Qemu-devel] [RISU PATCH v3 01/18] risugen_common: add helper functions insnv, randint

[Jan Bobek <jan.bobek@gmail.com>]

insnv allows emitting variable-length instructions in little-endian or
big-endian byte order; it subsumes functionality of former insn16()
and insn32() functions.

randint can reliably generate signed or unsigned integers of arbitrary
width.

Signed-off-by: Jan Bobek <jan.bobek@gmail.com>
---
 risugen_common.pm | 55 +++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 48 insertions(+), 7 deletions(-)

diff --git a/risugen_common.pm b/risugen_common.pm
index 71ee996..d63250a 100644
--- a/risugen_common.pm
+++ b/risugen_common.pm
@@ -23,8 +23,9 @@ BEGIN {
     require Exporter;
 
     our @ISA = qw(Exporter);
-    our @EXPORT = qw(open_bin close_bin set_endian insn32 insn16 $bytecount
-                   progress_start progress_update progress_end
+    our @EXPORT = qw(open_bin close_bin set_endian insn32 insn16
+                   $bytecount insnv randint progress_start
+                   progress_update progress_end
                    eval_with_fields is_pow_of_2 sextract ctz
                    dump_insn_details);
 }
@@ -37,7 +38,7 @@ my $bigendian = 0;
 # (default is little endian, 0).
 sub set_endian
 {
-    $bigendian = @_;
+    ($bigendian) = @_;
 }
 
 sub open_bin
@@ -52,18 +53,58 @@ sub close_bin
     close(BIN) or die "can't close output file: $!";
 }
 
+sub insnv(%)
+{
+    my (%args) = @_;
+
+    # Default to big-endian order, so that the instruction bytes are
+    # emitted in the same order as they are written in the
+    # configuration file.
+    $args{bigendian} = 1 unless defined $args{bigendian};
+
+    for (my $bitcur = 0; $bitcur < $args{width}; $bitcur += 8) {
+        my $value = $args{value} >> ($args{bigendian}
+                                     ? $args{width} - $bitcur - 8
+                                     : $bitcur);
+
+        print BIN pack("C", $value & 0xff);
+        $bytecount += 1;
+    }
+}
+
 sub insn32($)
 {
     my ($insn) = @_;
-    print BIN pack($bigendian ? "N" : "V", $insn);
-    $bytecount += 4;
+    insnv(value => $insn, width => 32, bigendian => $bigendian);
 }
 
 sub insn16($)
 {
     my ($insn) = @_;
-    print BIN pack($bigendian ? "n" : "v", $insn);
-    $bytecount += 2;
+    insnv(value => $insn, width => 16, bigendian => $bigendian);
+}
+
+sub randint
+{
+    my (%args) = @_;
+    my $width = $args{width};
+
+    if ($width > 32) {
+        # Generate at most 32 bits at once; Perl's rand() does not
+        # behave well with ranges that are too large.
+        my $lower = randint(%args, width => 32);
+        my $upper = randint(%args, width => $args{width} - 32);
+        # Use arithmetic rather than bitwise operators, since bitwise
+        # ops turn signed integers into unsigned.
+        return $upper * (1 << 32) + $lower;
+    } elsif ($width > 0) {
+        my $halfrange = 1 << ($width - 1);
+        my $value = int(rand(2 * $halfrange));
+        $value -= $halfrange if defined $args{signed} && $args{signed};
+        return $value;
+    } else {
+        return 0;
+    }
 }
 
 # Progress bar implementation
-- 
2.20.1