The functional overlap between the single- and double-word functions makes
functions makes this implementation about half the size of the C functions
if both functions are linked in the same application.
gcc/libgcc/ChangeLog:
2021-01-13 Daniel Engel <g...@danielengel.com>
* config/arm/parity.S: New file for __paritysi2/di2().
* config/arm/lib1funcs.S: #include bit/parity.S
* config/arm/t-elf (LIB1ASMFUNCS): Added _paritysi2/di2.
---
libgcc/config/arm/lib1funcs.S | 1 +
libgcc/config/arm/parity.S | 120 ++++++++++++++++++++++++++++++++++
libgcc/config/arm/t-elf | 2 +
3 files changed, 123 insertions(+)
create mode 100644 libgcc/config/arm/parity.S
diff --git a/libgcc/config/arm/lib1funcs.S b/libgcc/config/arm/lib1funcs.S
index 7ac50230725..600ea2dfdc9 100644
--- a/libgcc/config/arm/lib1funcs.S
+++ b/libgcc/config/arm/lib1funcs.S
@@ -1704,6 +1704,7 @@ LSYM(Lover12):
#include "clz2.S"
#include "ctz2.S"
+#include "parity.S"
/* ------------------------------------------------------------------------ */
/* These next two sections are here despite the fact that they contain Thumb
diff --git a/libgcc/config/arm/parity.S b/libgcc/config/arm/parity.S
new file mode 100644
index 00000000000..45233bc9d8f
--- /dev/null
+++ b/libgcc/config/arm/parity.S
@@ -0,0 +1,120 @@
+/* parity.S: ARM optimized parity functions
+
+ Copyright (C) 2020-2021 Free Software Foundation, Inc.
+ Contributed by Daniel Engel (g...@danielengel.com)
+
+ This file is free software; you can redistribute it and/or modify it
+ under the terms of the GNU General Public License as published by the
+ Free Software Foundation; either version 3, or (at your option) any
+ later version.
+
+ This file 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. See the GNU
+ General Public License for more details.
+
+ Under Section 7 of GPL version 3, you are granted additional
+ permissions described in the GCC Runtime Library Exception, version
+ 3.1, as published by the Free Software Foundation.
+
+ You should have received a copy of the GNU General Public License and
+ a copy of the GCC Runtime Library Exception along with this program;
+ see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
+ <http://www.gnu.org/licenses/>. */
+
+
+#ifdef L_paritydi2
+
+// int __paritydi2(int)
+// Returns '0' if the number of bits set in $r1:r0 is even, and '1' otherwise.
+// Returns the result in $r0.
+FUNC_START_SECTION paritydi2 .text.sorted.libgcc.paritydi2
+ CFI_START_FUNCTION
+
+ // Combine the upper and lower words, then fall through.
+ // Byte-endianness does not matter for this function.
+ eors r0, r1
+
+#endif /* L_paritydi2 */
+
+
+// The implementation of __paritydi2() tightly couples with __paritysi2(),
+// such that instructions must appear consecutively in the same memory
+// section for proper flow control. However, this construction inhibits
+// the ability to discard __paritydi2() when only using __paritysi2().
+// Therefore, this block configures __paritysi2() for compilation twice.
+// The first version is a minimal standalone implementation, and the second
+// version is the continuation of __paritydi2(). The standalone version must
+// be declared WEAK, so that the combined version can supersede it and
+// provide both symbols when required.
+// '_paritysi2' should appear before '_paritydi2' in LIB1ASMFUNCS.
+#if defined(L_paritysi2) || defined(L_paritydi2)
+
+#ifdef L_paritysi2
+// int __paritysi2(int)
+// Returns '0' if the number of bits set in $r0 is even, and '1' otherwise.
+// Returns the result in $r0.
+// Uses $r2 as scratch space.
+WEAK_START_SECTION paritysi2 .text.sorted.libgcc.paritysi2
+ CFI_START_FUNCTION
+
+#else /* L_paritydi2 */
+FUNC_ENTRY paritysi2
+
+#endif
+
+ #if defined(__thumb__) && __thumb__
+ #if defined(__OPTIMIZE_SIZE__) && __OPTIMIZE_SIZE__
+
+ // Size optimized: 16 bytes, 40 cycles
+ // Speed optimized: 24 bytes, 14 cycles
+ movs r2, #16
+
+ LLSYM(__parity_loop):
+ // Calculate the parity of successively smaller half-words into the
MSB.
+ movs r1, r0
+ lsls r1, r2
+ eors r0, r1
+ lsrs r2, #1
+ bne LLSYM(__parity_loop)
+
+ #else /* !__OPTIMIZE_SIZE__ */
+
+ // Unroll the loop. The 'libgcc' reference C implementation replaces
+ // the x2 and the x1 shifts with a constant. However, since it takes
+ // 4 cycles to load, index, and mask the constant result, it doesn't
+ // cost anything to keep shifting (and saves a few bytes).
+ lsls r1, r0, #16
+ eors r0, r1
+ lsls r1, r0, #8
+ eors r0, r1
+ lsls r1, r0, #4
+ eors r0, r1
+ lsls r1, r0, #2
+ eors r0, r1
+ lsls r1, r0, #1
+ eors r0, r1
+
+ #endif /* !__OPTIMIZE_SIZE__ */
+ #else /* !__thumb__ */
+
+ eors r0, r0, r0, lsl #16
+ eors r0, r0, r0, lsl #8
+ eors r0, r0, r0, lsl #4
+ eors r0, r0, r0, lsl #2
+ eors r0, r0, r0, lsl #1
+
+ #endif /* !__thumb__ */
+
+ lsrs r0, #31
+ RET
+
+ CFI_END_FUNCTION
+FUNC_END paritysi2
+
+#ifdef L_paritydi2
+FUNC_END paritydi2
+#endif
+
+#endif /* L_paritysi2 || L_paritydi2 */
+
diff --git a/libgcc/config/arm/t-elf b/libgcc/config/arm/t-elf
index 346fc766f17..0e9b9ce21af 100644
--- a/libgcc/config/arm/t-elf
+++ b/libgcc/config/arm/t-elf
@@ -24,6 +24,7 @@ endif # !__symbian__
LIB1ASMFUNCS += \
_clzsi2 \
_ctzsi2 \
+ _paritysi2 \
# Group 1: Integer function objects.
@@ -37,6 +38,7 @@ LIB1ASMFUNCS += \
_ctzdi2 \
_ffssi2 \
_ffsdi2 \
+ _paritydi2 \
_dvmd_tls \
_divsi3 \
_modsi3 \
--
2.25.1
