[PATCH] newlib/libc/stdbit: Fix static assertions for 16-bit int

[Jonathan Wakely]

All the USHRT_WIDTH < UINT_WIDTH assertions fail for 16-bit int targets,
such as msp430-elf. Remove those static assertions and instead fix the
stdc_xxx_us functions to work correctly when USHRT_WIDTH == UINT_WIDTH.

Signed-off-by: Jonathan Wakely <jwakely@redhat.com>
---

This is untested, except to check that it now compiles on msp430-elf and
still compiles on arm-eabi.

 newlib/libc/stdbit/stdc_bit_ceil.c       |  9 +++++----
 newlib/libc/stdbit/stdc_leading_ones.c   | 10 ++++++----
 newlib/libc/stdbit/stdc_leading_zeros.c  | 10 ++++++----
 newlib/libc/stdbit/stdc_trailing_ones.c  | 10 ++++++----
 newlib/libc/stdbit/stdc_trailing_zeros.c | 11 +++++++----
 5 files changed, 30 insertions(+), 20 deletions(-)

diff --git a/newlib/libc/stdbit/stdc_bit_ceil.c b/newlib/libc/stdbit/stdc_bit_ceil.c
index f25d184af..7ffed05f4 100644
--- a/newlib/libc/stdbit/stdc_bit_ceil.c
+++ b/newlib/libc/stdbit/stdc_bit_ceil.c
@@ -23,16 +23,17 @@ stdc_bit_ceil_uc(unsigned char x)
 	return (1U << (UINT_WIDTH - __builtin_clz(x - 1)));
 }
 
-/* Ensure we don't shift 1U out of range. */
-_Static_assert(USHRT_WIDTH < UINT_WIDTH,
-    "stdc_bit_ceil_us needs USHRT_WIDTH < UINT_WIDTH");
-
 unsigned short
 stdc_bit_ceil_us(unsigned short x)
 {
 	if (x <= 1)
 		return (1);
 
+#if USHRT_WIDTH == UINT_WIDTH
+	if (x > USHRT_MAX/2 + 1)
+		return (0);
+#endif
+
 	return (1U << (UINT_WIDTH - __builtin_clz(x - 1)));
 }
 
diff --git a/newlib/libc/stdbit/stdc_leading_ones.c b/newlib/libc/stdbit/stdc_leading_ones.c
index c7ab75b98..48f61d71e 100644
--- a/newlib/libc/stdbit/stdc_leading_ones.c
+++ b/newlib/libc/stdbit/stdc_leading_ones.c
@@ -22,13 +22,15 @@ stdc_leading_ones_uc(unsigned char x)
 	return (__builtin_clz(~(x << offset)));
 }
 
-/* Avoid triggering undefined behavior if x == 0. */
-_Static_assert(USHRT_WIDTH < UINT_WIDTH,
-    "stdc_leading_ones_us needs USHRT_WIDTH < UINT_WIDTH");
-
 unsigned int
 stdc_leading_ones_us(unsigned short x)
 {
+#if USHRT_WIDTH == UINT_WIDTH
+	/* Avoid triggering undefined behavior if x == 0. */
+	if (x == ~0U)
+		return (USHRT_WIDTH);
+#endif
+
 	const int offset = UINT_WIDTH - USHRT_WIDTH;
 
 	return (__builtin_clz(~(x << offset)));
diff --git a/newlib/libc/stdbit/stdc_leading_zeros.c b/newlib/libc/stdbit/stdc_leading_zeros.c
index dba6a14e2..204f71e21 100644
--- a/newlib/libc/stdbit/stdc_leading_zeros.c
+++ b/newlib/libc/stdbit/stdc_leading_zeros.c
@@ -22,13 +22,15 @@ stdc_leading_zeros_uc(unsigned char x)
 	return (__builtin_clz((x << offset) + (1U << (offset - 1))));
 }
 
-/* Offset must be greater than zero. */
-_Static_assert(USHRT_WIDTH < UINT_WIDTH,
-    "stdc_leading_zeros_us needs USHRT_WIDTH < UINT_WIDTH");
-
 unsigned int
 stdc_leading_zeros_us(unsigned short x)
 {
+#if USHRT_WIDTH == UINT_WIDTH
+	/* Offset must be greater than zero. */
+	if (x == 0)
+		return (USHRT_WIDTH);
+#endif
+
 	const int offset = UINT_WIDTH - USHRT_WIDTH;
 
 	return (__builtin_clz((x << offset) + (1U << (offset - 1))));
diff --git a/newlib/libc/stdbit/stdc_trailing_ones.c b/newlib/libc/stdbit/stdc_trailing_ones.c
index 0f7ccb553..22f002878 100644
--- a/newlib/libc/stdbit/stdc_trailing_ones.c
+++ b/newlib/libc/stdbit/stdc_trailing_ones.c
@@ -20,13 +20,15 @@ stdc_trailing_ones_uc(unsigned char x)
 	return (__builtin_ctz(~x));
 }
 
-/* Avoid triggering undefined behavior if x == ~0. */
-_Static_assert(USHRT_WIDTH < UINT_WIDTH,
-    "stdc_trailing_ones_uc needs USHRT_WIDTH < UINT_WIDTH");
-
 unsigned int
 stdc_trailing_ones_us(unsigned short x)
 {
+#if USHRT_WIDTH == UINT_WIDTH
+	/* Avoid triggering undefined behavior if x == ~0. */
+	if (x == ~0U)
+		return (USHRT_WIDTH);
+#endif
+
 	return (__builtin_ctz(~x));
 }
 
diff --git a/newlib/libc/stdbit/stdc_trailing_zeros.c b/newlib/libc/stdbit/stdc_trailing_zeros.c
index 396333e17..8526461bc 100644
--- a/newlib/libc/stdbit/stdc_trailing_zeros.c
+++ b/newlib/libc/stdbit/stdc_trailing_zeros.c
@@ -20,14 +20,17 @@ stdc_trailing_zeros_uc(unsigned char x)
 	return (__builtin_ctz(x | 1U << UCHAR_WIDTH));
 }
 
-/* Ensure we do not shift 1U out of range. */
-_Static_assert(USHRT_WIDTH < UINT_WIDTH,
-    "stdc_trailing_zeros_uc needs USHRT_WIDTH < UINT_WIDTH");
-
 unsigned int
 stdc_trailing_zeros_us(unsigned short x)
 {
+#if USHRT_WIDTH == UINT_WIDTH
+	/* Ensure we do not shift 1U out of range. */
+	if (x == 0U)
+		return (USHRT_WIDTH);
+	return (__builtin_ctz(x));
+#else
 	return (__builtin_ctz(x | 1U << USHRT_WIDTH));
+#endif
 }
 
 unsigned int
-- 
2.53.0