MP3Decoder: Request defined behavior for signed integer shifts

jepler · jepler · commit 34a46de3eb5c · 2024-05-01T14:21:03.000-05:00
gcc -fsanitize=undefined reports diagnostics like these:
```
../../src/bitstream.c:93:36: runtime error: left shift of 177 by 24 places cannot be represented in type 'int'
../../src/imdct.c:86:53: runtime error: left shift of negative value -937
```

-fwrapv provides implementation-defined behavior that matches the expectations of two's complement arithmetic.
diff --git a/py/circuitpy_defns.mk b/py/circuitpy_defns.mk
@@ -782,7 +782,7 @@ SRC_MOD += $(addprefix lib/mp3/src/, \
 	subband.c \
 	trigtabs.c \
 )
-$(BUILD)/lib/mp3/src/buffers.o: CFLAGS += -include "shared-module/audiomp3/__init__.h" -D'MPDEC_ALLOCATOR(x)=mp3_alloc(x)' -D'MPDEC_FREE(x)=mp3_free(x)'
+$(BUILD)/lib/mp3/src/buffers.o: CFLAGS += -include "shared-module/audiomp3/__init__.h" -D'MPDEC_ALLOCATOR(x)=mp3_alloc(x)' -D'MPDEC_FREE(x)=mp3_free(x)' -fwrapv
 ifeq ($(CIRCUITPY_AUDIOMP3_USE_PORT_ALLOCATOR),1)
 SRC_COMMON_HAL_ALL += \
 	audiomp3/__init__.c

Original file line number	Diff line number	Diff line change
`@@ -782,7 +782,7 @@ SRC_MOD += $(addprefix lib/mp3/src/, \`
`782`	`782`	`subband.c \`
`783`	`783`	`trigtabs.c \`
`784`	`784`	`)`
`785`		`-$(BUILD)/lib/mp3/src/buffers.o: CFLAGS += -include "shared-module/audiomp3/__init__.h" -D'MPDEC_ALLOCATOR(x)=mp3_alloc(x)' -D'MPDEC_FREE(x)=mp3_free(x)'`
	`785`	`+$(BUILD)/lib/mp3/src/buffers.o: CFLAGS += -include "shared-module/audiomp3/__init__.h" -D'MPDEC_ALLOCATOR(x)=mp3_alloc(x)' -D'MPDEC_FREE(x)=mp3_free(x)' -fwrapv`
`786`	`786`	`ifeq ($(CIRCUITPY_AUDIOMP3_USE_PORT_ALLOCATOR),1)`
`787`	`787`	`SRC_COMMON_HAL_ALL += \`
`788`	`788`	`audiomp3/__init__.c`