[Qemu-devel] [PATCH v4] bitops.h: Add functions to extract and deposit bitfields

[Peter Maydell <peter.maydell@linaro.org>]

Add functions deposit32(), deposit64(), extract32() and extract64()
to extract and deposit bitfields in 32 and 64 bit words. Based on
ideas by Jia Liu and Avi Kivity.

Suggested-by: Jia Liu <proljc@gmail.com>
Suggested-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Andreas Färber <afaerber@suse.de>
---
Changes:
 v1->v2: added missing brackets
 v2->v3: renamed field32,field64 to extract32,extract64
         added deposit32,deposit64 at Avi's suggestion
         fixed assertion as per Jay Foad's suggestion
 v3->v4: fixed gtk-doc comment formats, expanded doc comments slightly

I took the liberty of leaving Eric and Andreas' Reviewed-by: tags
on since there are no code changes in v4, only doc comments.

 bitops.h |   90 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 90 insertions(+), 0 deletions(-)

diff --git a/bitops.h b/bitops.h
index 07d1a06..b967ef3 100644
--- a/bitops.h
+++ b/bitops.h
@@ -269,4 +269,94 @@ static inline unsigned long hweight_long(unsigned long w)
     return count;
 }
 
+/**
+ * extract32:
+ * @value: the value to extract the bit field from
+ * @start: the lowest bit in the bit field (numbered from 0)
+ * @length: the length of the bit field
+ *
+ * Extract from the 32 bit input @value the bit field specified by the
+ * @start and @length parameters, and return it. The bit field must
+ * lie entirely within the 32 bit word. It is valid to request that
+ * all 32 bits are returned (ie @length 32 and @start 0).
+ *
+ * Returns: the value of the bit field extracted from the input value.
+ */
+static inline uint32_t extract32(uint32_t value, int start, int length)
+{
+    assert(start >= 0 && length > 0 && length <= 32 - start);
+    return (value >> start) & (~0U >> (32 - length));
+}
+
+/**
+ * extract64:
+ * @value: the value to extract the bit field from
+ * @start: the lowest bit in the bit field (numbered from 0)
+ * @length: the length of the bit field
+ *
+ * Extract from the 64 bit input @value the bit field specified by the
+ * @start and @length parameters, and return it. The bit field must
+ * lie entirely within the 64 bit word. It is valid to request that
+ * all 64 bits are returned (ie @length 64 and @start 0).
+ *
+ * Returns: the value of the bit field extracted from the input value.
+ */
+static inline uint64_t extract64(uint64_t value, int start, int length)
+{
+    assert(start >= 0 && length > 0 && length <= 64 - start);
+    return (value >> start) & (~0ULL >> (64 - length));
+}
+
+/**
+ * deposit32:
+ * @value: initial value to insert bit field into
+ * @start: the lowest bit in the bit field (numbered from 0)
+ * @length: the length of the bit field
+ * @fieldval: the value to insert into the bit field
+ *
+ * Deposit @fieldval into the 32 bit @value at the bit field specified
+ * by the @start and @length parameters, and return the modified
+ * @value. Bits of @value outside the bit field are not modified.
+ * Bits of @fieldval above the least significant @length bits are
+ * ignored. The bit field must lie entirely within the 32 bit word.
+ * It is valid to request that all 64 bits are modified (ie @length
+ * 64 and @start 0).
+ *
+ * Returns: the modified @value.
+ */
+static inline uint32_t deposit32(uint32_t value, int start, int length,
+                                 uint32_t fieldval)
+{
+    uint32_t mask;
+    assert(start >= 0 && length > 0 && length <= 32 - start);
+    mask = (~0U >> (32 - length)) << start;
+    return (value & ~mask) | ((fieldval << start) & mask);
+}
+
+/**
+ * deposit32:
+ * @value: initial value to insert bit field into
+ * @start: the lowest bit in the bit field (numbered from 0)
+ * @length: the length of the bit field
+ * @fieldval: the value to insert into the bit field
+ *
+ * Deposit @fieldval into the 64 bit @value at the bit field specified
+ * by the @start and @length parameters, and return the modified
+ * @value. Bits of @value outside the bit field are not modified.
+ * Bits of @fieldval above the least significant @length bits are
+ * ignored. The bit field must lie entirely within the 32 bit word.
+ * It is valid to request that all 64 bits are modified (ie @length
+ * 64 and @start 0).
+ *
+ * Returns: the modified @value.
+ */
+static inline uint64_t deposit64(uint64_t value, int start, int length,
+                                 uint64_t fieldval)
+{
+    uint64_t mask;
+    assert(start >= 0 && length > 0 && length <= 64 - start);
+    mask = (~0ULL >> (64 - length)) << start;
+    return (value & ~mask) | ((fieldval << start) & mask);
+}
+
 #endif
-- 
1.7.1