include/linux/kernel.h: change abs() macro so it uses consistent return type

Rewrite abs() so that its return type does not depend on the
architecture and no unexpected type conversion happen inside of it.  The
only conversion is from unsigned to signed type.  char is left as a
return type but treated as a signed type regradless of it's actual
signedness.

With the old version, int arguments were promoted to long and depending
on architecture a long argument might result in s64 or long return type
(which may or may not be the same).

This came after some back and forth with Nicolas.  The current macro has
different return type (for the same input type) depending on
architecture which might be midly iritating.

An alternative version would promote to int like so:

	#define abs(x)	__abs_choose_expr(x, long long,			\
			__abs_choose_expr(x, long,			\
			__builtin_choose_expr(				\
				sizeof(x) <= sizeof(int),		\
				({ int __x = (x); __x<0?-__x:__x; }),	\
				((void)0))))

I have no preference but imagine Linus might.  :] Nicolas argument against
is that promoting to int causes iconsistent behaviour:

	int main(void) {
		unsigned short a = 0, b = 1, c = a - b;
		unsigned short d = abs(a - b);
		unsigned short e = abs(c);
		printf("%u %u\n", d, e);  // prints: 1 65535
	}

Then again, no sane person expects consistent behaviour from C integer
arithmetic.  ;)

Note:

  __builtin_types_compatible_p(unsigned char, char) is always false, and
  __builtin_types_compatible_p(signed char, char) is also always false.

Signed-off-by: Michal Nazarewicz <mina86@mina86.com>
Reviewed-by: Nicolas Pitre <nico@linaro.org>
Cc: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Cc: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
index fd01f3493fc7792792d015c604903197ba506073..af7cc1e65656e1bf0ac83f561945bbbcf45d9de9 100644 (file)
--- a/drivers/iio/industrialio-core.c
+++ b/drivers/iio/industrialio-core.c
@@ -433,16 +433,15 @@ ssize_t iio_format_value(char *buf, unsigned int type, int size, int *vals)
                scale_db = true;
        case IIO_VAL_INT_PLUS_MICRO:
                if (vals[1] < 0)
-                       return sprintf(buf, "-%ld.%06u%s\n", abs(vals[0]),
-                                       -vals[1],
-                               scale_db ? " dB" : "");
+                       return sprintf(buf, "-%d.%06u%s\n", abs(vals[0]),
+                                      -vals[1], scale_db ? " dB" : "");
                else
                        return sprintf(buf, "%d.%06u%s\n", vals[0], vals[1],
                                scale_db ? " dB" : "");
        case IIO_VAL_INT_PLUS_NANO:
                if (vals[1] < 0)
-                       return sprintf(buf, "-%ld.%09u\n", abs(vals[0]),
-                                       -vals[1]);
+                       return sprintf(buf, "-%d.%09u\n", abs(vals[0]),
+                                      -vals[1]);
                else
                        return sprintf(buf, "%d.%09u\n", vals[0], vals[1]);
        case IIO_VAL_FRACTIONAL:

diff --git a/drivers/net/wireless/intel/iwlwifi/dvm/calib.c b/drivers/net/wireless/intel/iwlwifi/dvm/calib.c
index 07a4c644fb9be4b0aa3eef7f2ec889853eecd19c..e9cef9de9ed85fffbf02fd71219ffd57323e4a9a 100644 (file)
--- a/drivers/net/wireless/intel/iwlwifi/dvm/calib.c
+++ b/drivers/net/wireless/intel/iwlwifi/dvm/calib.c
@@ -901,7 +901,7 @@ static void iwlagn_gain_computation(struct iwl_priv *priv,
                /* bound gain by 2 bits value max, 3rd bit is sign */
                data->delta_gain_code[i] =
                        min(abs(delta_g),
-                       (long) CHAIN_NOISE_MAX_DELTA_GAIN_CODE);
+                       (s32) CHAIN_NOISE_MAX_DELTA_GAIN_CODE);
 
                if (delta_g < 0)
                        /*

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 7311c3294e25f22a610209a63115c3d0778ecd0b..f31638c6e8738230edebe2606ff27d8782fc1a19 100644 (file)
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -202,26 +202,26 @@ extern int _cond_resched(void);
 
 /**
  * abs - return absolute value of an argument
- * @x: the value.  If it is unsigned type, it is converted to signed type first
- *   (s64, long or int depending on its size).
+ * @x: the value.  If it is unsigned type, it is converted to signed type first.
+ *     char is treated as if it was signed (regardless of whether it really is)
+ *     but the macro's return type is preserved as char.
  *
- * Return: an absolute value of x.  If x is 64-bit, macro's return type is s64,
- *   otherwise it is signed long.
+ * Return: an absolute value of x.
  */
-#define abs(x) __builtin_choose_expr(sizeof(x) == sizeof(s64), ({      \
-               s64 __x = (x);                                          \
-               (__x < 0) ? -__x : __x;                                 \
-       }), ({                                                          \
-               long ret;                                               \
-               if (sizeof(x) == sizeof(long)) {                        \
-                       long __x = (x);                                 \
-                       ret = (__x < 0) ? -__x : __x;                   \
-               } else {                                                \
-                       int __x = (x);                                  \
-                       ret = (__x < 0) ? -__x : __x;                   \
-               }                                                       \
-               ret;                                                    \
-       }))
+#define abs(x) __abs_choose_expr(x, long long,                         \
+               __abs_choose_expr(x, long,                              \
+               __abs_choose_expr(x, int,                               \
+               __abs_choose_expr(x, short,                             \
+               __abs_choose_expr(x, char,                              \
+               __builtin_choose_expr(                                  \
+                       __builtin_types_compatible_p(typeof(x), char),  \
+                       (char)({ signed char __x = (x); __x<0?-__x:__x; }), \
+                       ((void)0)))))))
+
+#define __abs_choose_expr(x, type, other) __builtin_choose_expr(       \
+       __builtin_types_compatible_p(typeof(x),   signed type) ||       \
+       __builtin_types_compatible_p(typeof(x), unsigned type),         \
+       ({ signed type __x = (x); __x < 0 ? -__x : __x; }), other)
 
 /**
  * reciprocal_scale - "scale" a value into range [0, ep_ro)