From fc81f546bf409fad2f33c6c66d69d4c72d9904df Mon Sep 17 00:00:00 2001
From: Mikael Pettersson <mikpelinux@gmail.com>
Date: Thu, 14 Aug 2025 16:38:47 +0200
Subject: [PATCH] readelf: move uint36_from_s64 conversion to extint

---
 erlang/apps/lib/src/extint.erl      | 14 ++++++++++++++
 erlang/apps/readelf/src/readelf.erl | 13 ++-----------
 2 files changed, 16 insertions(+), 11 deletions(-)

diff --git a/erlang/apps/lib/src/extint.erl b/erlang/apps/lib/src/extint.erl
index 4f49d3a..90fde17 100644
--- a/erlang/apps/lib/src/extint.erl
+++ b/erlang/apps/lib/src/extint.erl
@@ -32,6 +32,7 @@
         , uint32_from_ext/1
         , uint32_to_ext/1
         , uint36_from_ext/1
+        , uint36_from_s64/1
         , uint36_to_c36/1
         , uint36_to_ext/1
         , uint64_from_ext/1
@@ -77,6 +78,19 @@ uint36_from_ext([B0, B1, B2, B3]) ->
   ((B2 band ?UINT9_MAX) bsl  9) bor
    (B3 band ?UINT9_MAX).
 
+%% S64 is the sparse representation of a 36-bit word in 64 bits where
+%% each 9-bit field is zero-extended to 16 bits, i.e. two octets.
+%% The PDP-10 port of GNU binutils uses this format.
+%% This converts S64-encoded data back to a 36-bit word.
+-spec uint36_from_s64([uint8_t()]) -> uint36_t().
+uint36_from_s64([B0, B1, B2, B3, B4, B5, B6, B7]) ->
+  0 = (B0 bor B2 bor B4 bor B6) band bnot 1, % assert
+  N0 = (B0 bsl 8) bor B1,
+  N1 = (B2 bsl 8) bor B3,
+  N2 = (B4 bsl 8) bor B5,
+  N3 = (B6 bsl 8) bor B7,
+  uint36_from_ext([N0, N1, N2, N3]).
+
 -spec uint36_to_ext(uint36_t()) -> [uint9_t()].
 uint36_to_ext(U36) ->
   [_B0 = (U36 bsr 27) band ?UINT9_MAX,
diff --git a/erlang/apps/readelf/src/readelf.erl b/erlang/apps/readelf/src/readelf.erl
index a1b1734..c6defc0 100644
--- a/erlang/apps/readelf/src/readelf.erl
+++ b/erlang/apps/readelf/src/readelf.erl
@@ -745,26 +745,17 @@ wordsize(_) -> 4.
 
 read_uint36({?ELFCLASS64, _} = FP) ->
   case libelf:fread(8, FP) of
-    {ok, [B0, B1, B2, B3, B4, B5, B6, B7]} ->
-      0 = (B0 bor B2 bor B4 bor B6) band bnot 1, % assert
-      N0 = (B0 bsl 8) bor B1,
-      N1 = (B2 bsl 8) bor B3,
-      N2 = (B4 bsl 8) bor B5,
-      N3 = (B6 bsl 8) bor B7,
-      {ok, make_uint36(N0, N1, N2, N3)};
+    {ok, Bytes} -> {ok, extint:uint36_from_s64(Bytes)};
     eof -> {error, eof};
     {error, _Reason} = Error -> Error
   end;
 read_uint36({?ELFCLASS36, _} = FP) ->
   case libelf:fread(4, FP) of
-    {ok, [N0, N1, N2, N3]} -> {ok, make_uint36(N0, N1, N2, N3)};
+    {ok, Nonets} -> {ok, extint:uint36_from_ext(Nonets)};
     eof -> {error, eof};
     {error, _Reason} = Error -> Error
   end.
 
-make_uint36(N0, N1, N2, N3) ->
-  (((((N0 bsl 9) bor N1) bsl 9) bor N2) bsl 9) bor N3.
-
 disassemble_insn(InsnWord) ->
   Models = ?PDP10_KL10_271up,
   High13 = InsnWord bsr (36 - 13),