From dc82c117f542c4ae4b084de349649c3e49873cc6 Mon Sep 17 00:00:00 2001
From: baldurk <baldurk@baldurk.org>
Date: Wed, 11 Mar 2026 22:43:24 +0000
Subject: [PATCH] Fix edge case of bitfield extract with count == numbits.
 Closes #3813

* This is only legal if offset is 0 and so degenerate, but it is valid and needs
  to be handled.
---
 .../driver/shaders/spirv/spirv_debug.cpp      | 23 ++++++++++---------
 util/test/demos/vk/vk_shader_debug_zoo.cpp    |  9 ++++++++
 2 files changed, 21 insertions(+), 11 deletions(-)

diff --git a/renderdoc/driver/shaders/spirv/spirv_debug.cpp b/renderdoc/driver/shaders/spirv/spirv_debug.cpp
index 681aef1a3..19dfbf1ea 100644
--- a/renderdoc/driver/shaders/spirv/spirv_debug.cpp
+++ b/renderdoc/driver/shaders/spirv/spirv_debug.cpp
@@ -2234,17 +2234,18 @@ void ThreadState::StepNext(bool useDebugState, const uint32_t steps,
       for(uint8_t c = 0; c < var.columns; c++)
       {
 #undef _IMPL
-#define _IMPL(I, S, U)                               \
-  const U mask = (U(1) << comp<U>(count, c)) - U(1); \
-                                                     \
-  comp<U>(var, c) >>= comp<U>(offset, c);            \
-  comp<U>(var, c) &= mask;                           \
-                                                     \
-  if(opdata.op == Op::BitFieldSExtract)              \
-  {                                                  \
-    U topbit = (mask + U(1)) >> U(1);                \
-    if(comp<U>(var, c) & topbit)                     \
-      comp<U>(var, c) |= (~0ULL ^ mask);             \
+#define _IMPL(I, S, U)                                                          \
+  const U bitcount = comp<U>(count, c);                                         \
+  const U mask = bitcount == sizeof(U) * 8 ? ~0ULL : (U(1) << bitcount) - U(1); \
+                                                                                \
+  comp<U>(var, c) >>= comp<U>(offset, c);                                       \
+  comp<U>(var, c) &= mask;                                                      \
+                                                                                \
+  if(opdata.op == Op::BitFieldSExtract)                                         \
+  {                                                                             \
+    U topbit = (mask + U(1)) >> U(1);                                           \
+    if(comp<U>(var, c) & topbit)                                                \
+      comp<U>(var, c) |= (~0ULL ^ mask);                                        \
   }
 
         IMPL_FOR_INT_TYPES(_IMPL);
diff --git a/util/test/demos/vk/vk_shader_debug_zoo.cpp b/util/test/demos/vk/vk_shader_debug_zoo.cpp
index 70cfbdf53..0e7dd82bf 100644
--- a/util/test/demos/vk/vk_shader_debug_zoo.cpp
+++ b/util/test/demos/vk/vk_shader_debug_zoo.cpp
@@ -1675,6 +1675,15 @@ void main()
       Color = vec4(x, y, z, w);
       break;
     }
+    case 187:
+    {
+      uint a = zerou + 0x44b82a80;
+      int b = zeroi + 0x44b82a80;
+
+      Color = vec4(float(bitfieldExtract(a, 0, 32)), float(bitfieldExtract(b, 0, 32)),
+                   float(bitfieldExtract(a, 32, 0)), float(bitfieldExtract(b, 32, 0)));
+      break;
+    }
     default: break;
   }
 }