--- /dev/null
+#ifndef _ASM_HASH_H
+#define _ASM_HASH_H
+
+/*
+ * HP-PA only implements integer multiply in the FPU. However, for
+ * integer multiplies by constant, it has a number of shift-and-add
+ * (but no shift-and-subtract, sigh!) instructions that a compiler
+ * can synthesize a code sequence with.
+ *
+ * Unfortunately, GCC isn't very efficient at using them. For example
+ * it uses three instructions for "x *= 21" when only two are needed.
+ * But we can find a sequence manually.
+ */
+
+#define HAVE_ARCH__HASH_32 1
+
+/*
+ * This is a multiply by GOLDEN_RATIO_32 = 0x61C88647 optimized for the
+ * PA7100 pairing rules. This is an in-order 2-way superscalar processor.
+ * Only one instruction in a pair may be a shift (by more than 3 bits),
+ * but other than that, simple ALU ops (including shift-and-add by up
+ * to 3 bits) may be paired arbitrarily.
+ *
+ * PA8xxx processors also dual-issue ALU instructions, although with
+ * fewer constraints, so this schedule is good for them, too.
+ *
+ * This 6-step sequence was found by Yevgen Voronenko's implementation
+ * of the Hcub algorithm at http://spiral.ece.cmu.edu/mcm/gen.html.
+ */
+static inline u32 __attribute_const__ __hash_32(u32 x)
+{
+ u32 a, b, c;
+
+ /*
+ * Phase 1: Compute a = (x << 19) + x,
+ * b = (x << 9) + a, c = (x << 23) + b.
+ */
+ a = x << 19; /* Two shifts can't be paired */
+ b = x << 9; a += x;
+ c = x << 23; b += a;
+ c += b;
+ /* Phase 2: Return (b<<11) + (c<<6) + (a<<3) - c */
+ b <<= 11;
+ a += c << 3; b -= c;
+ return (a << 3) + b;
+}
+
+#if BITS_PER_LONG == 64
+
+#define HAVE_ARCH_HASH_64 1
+
+/*
+ * Finding a good shift-and-add chain for GOLDEN_RATIO_64 is tricky,
+ * because available software for the purpose chokes on constants this
+ * large. (It's mostly designed for compiling FIR filter coefficients
+ * into FPGAs.)
+ *
+ * However, Jason Thong pointed out a work-around. The Hcub software
+ * (http://spiral.ece.cmu.edu/mcm/gen.html) is designed for *multiple*
+ * constant multiplication, and is good at finding shift-and-add chains
+ * which share common terms.
+ *
+ * Looking at 0x0x61C8864680B583EB in binary:
+ * 0110000111001000100001100100011010000000101101011000001111101011
+ * \______________/ \__________/ \_______/ \________/
+ * \____________________________/ \____________________/
+ * you can see the non-zero bits are divided into several well-separated
+ * blocks. Hcub can find algorithms for those terms separately, which
+ * can then be shifted and added together.
+ *
+ * Dividing the input into 2, 3 or 4 blocks, Hcub can find solutions
+ * with 10, 9 or 8 adds, respectively, making a total of 11 for the
+ * whole number.
+ *
+ * Using just two large blocks, 0xC3910C8D << 31 in the high bits,
+ * and 0xB583EB in the low bits, produces as good an algorithm as any,
+ * and with one more small shift than alternatives.
+ *
+ * The high bits are a larger number and more work to compute, as well
+ * as needing one extra cycle to shift left 31 bits before the final
+ * addition, so they are the critical path for scheduling. The low bits
+ * can fit into the scheduling slots left over.
+ */
+
+
+/*
+ * This _ASSIGN(dst, src) macro performs "dst = src", but prevents GCC
+ * from inferring anything about the value assigned to "dest".
+ *
+ * This prevents it from mis-optimizing certain sequences.
+ * In particular, gcc is annoyingly eager to combine consecutive shifts.
+ * Given "x <<= 19; y += x; z += x << 1;", GCC will turn this into
+ * "y += x << 19; z += x << 20;" even though the latter sequence needs
+ * an additional instruction and temporary register.
+ *
+ * Because no actual assembly code is generated, this construct is
+ * usefully portable across all GCC platforms, and so can be test-compiled
+ * on non-PA systems.
+ *
+ * In two places, additional unused input dependencies are added. This
+ * forces GCC's scheduling so it does not rearrange instructions too much.
+ * Because the PA-8xxx is out of order, I'm not sure how much this matters,
+ * but why make it more difficult for the processor than necessary?
+ */
+#define _ASSIGN(dst, src, ...) asm("" : "=r" (dst) : "0" (src), ##__VA_ARGS__)
+
+/*
+ * Multiply by GOLDEN_RATIO_64 = 0x0x61C8864680B583EB using a heavily
+ * optimized shift-and-add sequence.
+ *
+ * Without the final shift, the multiply proper is 19 instructions,
+ * 10 cycles and uses only 4 temporaries. Whew!
+ *
+ * You are not expected to understand this.
+ */
+static __always_inline u32 __attribute_const__
+hash_64(u64 a, unsigned int bits)
+{
+ u64 b, c, d;
+
+ /*
+ * Encourage GCC to move a dynamic shift to %sar early,
+ * thereby freeing up an additional temporary register.
+ */
+ if (!__builtin_constant_p(bits))
+ asm("" : "=q" (bits) : "0" (64 - bits));
+ else
+ bits = 64 - bits;
+
+ _ASSIGN(b, a*5); c = a << 13;
+ b = (b << 2) + a; _ASSIGN(d, a << 17);
+ a = b + (a << 1); c += d;
+ d = a << 10; _ASSIGN(a, a << 19);
+ d = a - d; _ASSIGN(a, a << 4, "X" (d));
+ c += b; a += b;
+ d -= c; c += a << 1;
+ a += c << 3; _ASSIGN(b, b << (7+31), "X" (c), "X" (d));
+ a <<= 31; b += d;
+ a += b;
+ return a >> bits;
+}
+#undef _ASSIGN /* We're a widely-used header file, so don't litter! */
+
+#endif /* BITS_PER_LONG == 64 */
+
+#endif /* _ASM_HASH_H */
}
static const struct iomap_ops ioport_ops = {
- ioport_read8,
- ioport_read16,
- ioport_read16,
- ioport_read32,
- ioport_read32,
- ioport_write8,
- ioport_write16,
- ioport_write16,
- ioport_write32,
- ioport_write32,
- ioport_read8r,
- ioport_read16r,
- ioport_read32r,
- ioport_write8r,
- ioport_write16r,
- ioport_write32r,
+ .read8 = ioport_read8,
+ .read16 = ioport_read16,
+ .read16be = ioport_read16,
+ .read32 = ioport_read32,
+ .read32be = ioport_read32,
+ .write8 = ioport_write8,
+ .write16 = ioport_write16,
+ .write16be = ioport_write16,
+ .write32 = ioport_write32,
+ .write32be = ioport_write32,
+ .read8r = ioport_read8r,
+ .read16r = ioport_read16r,
+ .read32r = ioport_read32r,
+ .write8r = ioport_write8r,
+ .write16r = ioport_write16r,
+ .write32r = ioport_write32r,
};
/* Legacy I/O memory ops */
}
static const struct iomap_ops iomem_ops = {
- iomem_read8,
- iomem_read16,
- iomem_read16be,
- iomem_read32,
- iomem_read32be,
- iomem_write8,
- iomem_write16,
- iomem_write16be,
- iomem_write32,
- iomem_write32be,
- iomem_read8r,
- iomem_read16r,
- iomem_read32r,
- iomem_write8r,
- iomem_write16r,
- iomem_write32r,
+ .read8 = iomem_read8,
+ .read16 = iomem_read16,
+ .read16be = iomem_read16be,
+ .read32 = iomem_read32,
+ .read32be = iomem_read32be,
+ .write8 = iomem_write8,
+ .write16 = iomem_write16,
+ .write16be = iomem_write16be,
+ .write32 = iomem_write32,
+ .write32be = iomem_write32be,
+ .read8r = iomem_read8r,
+ .read16r = iomem_read16r,
+ .read32r = iomem_read32r,
+ .write8r = iomem_write8r,
+ .write16r = iomem_write16r,
+ .write32r = iomem_write32r,
};
static const struct iomap_ops *iomap_ops[8] = {
projects / cascardo / linux.git / commitdiff