py/misc: Fix fallback implementation of mp_popcount.

dpgeorge · dpgeorge · commit 6fee099cae58 · 2025-06-25T11:36:28.000+10:00
Tested using gcc 7.3.1 which does not have the popcount built-in and uses
this fallback version.  Without the fix, mpy-cross produces mpy files with
corrupt RISC-V machine code.  With the fix, mpy-cross output is correct.

Signed-off-by: Damien George &lt;damien@micropython.org&gt;
diff --git a/py/misc.h b/py/misc.h
@@ -390,7 +390,7 @@ static inline uint32_t mp_popcount(uint32_t x) {
     x = x - ((x >> 1) & 0x55555555);
     x = (x & 0x33333333) + ((x >> 2) & 0x33333333);
     x = (x + (x >> 4)) & 0x0F0F0F0F;
-    return x * 0x01010101;
+    return (x * 0x01010101) >> 24;
 }
 #endif
 #endif

Original file line number	Diff line number	Diff line change
`@@ -390,7 +390,7 @@ static inline uint32_t mp_popcount(uint32_t x) {`
`390`	`390`	`x = x - ((x >> 1) & 0x55555555);`
`391`	`391`	`x = (x & 0x33333333) + ((x >> 2) & 0x33333333);`
`392`	`392`	`x = (x + (x >> 4)) & 0x0F0F0F0F;`
`393`		`- return x * 0x01010101;`
	`393`	`+ return (x * 0x01010101) >> 24;`
`394`	`394`	`}`
`395`	`395`	`#endif`
`396`	`396`	`#endif`