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--- do-while-0 [February 18, 2026 at 12:46] – created yanevskiv
+++ do-while-0 [May 14, 2026 at 11:38] (current) – external edit 127.0.0.1
@@ Line 1: / Line 1: @@
+# do { ... } while (0)
+In C programming language,`do { ... } while (0)` is a loop which does a single iteration. A compiler will optimize it away completely, so the syntax produces no actual machine code.
+Most commonly, it's used to make [[function-macro|function-macros]].
+Example:
+```c
+/*
+ * - clearing psr.i is implicitly serialized (visible by next insn)
+ * - setting psr.i requires data serialization
+ * - we need a stop-bit before reading PSR because we sometimes
+ *   write a floating-point register right before reading the PSR
+ *   and that writes to PSR.mfl
+ */
+#define __local_irq_save(x)         \
+do {                    \
+    ia64_stop();                \
+    (x) = ia64_getreg(_IA64_REG_PSR);   \
+    ia64_stop();                \
+    ia64_rsm(IA64_PSR_I);           \
+} while (0)
+```
+## Links
+ - https://stackoverflow.com/questions/2381300/what-does-do-while-0-do-exactly-in-kernel-code