Added bsr.h.

1 files changed, 61 insertions, 0 deletions

diff --git a/src/liblzma/common/bsr.h b/src/liblzma/common/bsr.h
new file mode 100644
index 00000000..fd5d3b04
--- /dev/null
+++ b/src/liblzma/common/bsr.h
@@ -0,0 +1,61 @@
+///////////////////////////////////////////////////////////////////////////////
+//
+/// \file       bsr.h
+/// \brief      Bit scan reverse
+//
+//  This code has been put into the public domain.
+//
+//  This library is distributed in the hope that it will be useful,
+//  but WITHOUT ANY WARRANTY; without even the implied warranty of
+//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+//
+///////////////////////////////////////////////////////////////////////////////
+
+#ifndef LZMA_BSR_H
+#define LZMA_BSR_H
+
+// NOTE: Both input and output variables for lzma_bsr must be uint32_t.
+
+#if defined(__GNUC__) && (defined (HAVE_ASM_X86) || defined(HAVE_ASM_X86_64))
+#	define lzma_bsr(dest, n) \
+		__asm__("bsrl %1, %0" : "=r" (dest) : "rm" (n))
+
+#else
+#	define lzma_bsr(dest, n) dest = lzma_bsr_helper(n)
+
+static inline uint32_t
+lzma_bsr_helper(uint32_t n)
+{
+	assert(n != 0);
+
+	uint32_t i = 31;
+
+	if ((n & UINT32_C(0xFFFF0000)) == 0) {
+		n <<= 16;
+		i = 15;
+	}
+
+	if ((n & UINT32_C(0xFF000000)) == 0) {
+		n <<= 8;
+		i -= 8;
+	}
+
+	if ((n & UINT32_C(0xF0000000)) == 0) {
+		n <<= 4;
+		i -= 4;
+	}
+
+	if ((n & UINT32_C(0xC0000000)) == 0) {
+		n <<= 2;
+		i -= 2;
+	}
+
+	if ((n & UINT32_C(0x80000000)) == 0)
+		--i;
+
+	return i;
+}
+
+#endif
+
+#endif