diff options
Diffstat (limited to 'src/hash/crc32/gen_const_ppc64le.go')
| -rw-r--r-- | src/hash/crc32/gen_const_ppc64le.go | 150 |
1 files changed, 150 insertions, 0 deletions
diff --git a/src/hash/crc32/gen_const_ppc64le.go b/src/hash/crc32/gen_const_ppc64le.go new file mode 100644 index 0000000..d7af018 --- /dev/null +++ b/src/hash/crc32/gen_const_ppc64le.go @@ -0,0 +1,150 @@ +// Copyright 2017 The Go Authors. All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +// +build ignore + +// Generate the constant table associated with the poly used by the +// vpmsumd crc32 algorithm. +// +// go run gen_const_ppc64le.go +// +// generates crc32_table_ppc64le.s + +// The following is derived from code written by Anton Blanchard +// <anton@au.ibm.com> found at https://github.com/antonblanchard/crc32-vpmsum. +// The original is dual licensed under GPL and Apache 2. As the copyright holder +// for the work, IBM has contributed this new work under the golang license. + +// This code was written in Go based on the original C implementation. + +// This is a tool needed to generate the appropriate constants needed for +// the vpmsum algorithm. It is included to generate new constant tables if +// new polynomial values are included in the future. + +package main + +import ( + "bytes" + "fmt" + "os" +) + +var blocking = 32 * 1024 + +func reflect_bits(b uint64, nr uint) uint64 { + var ref uint64 + + for bit := uint64(0); bit < uint64(nr); bit++ { + if (b & uint64(1)) == 1 { + ref |= (1 << (uint64(nr-1) - bit)) + } + b = (b >> 1) + } + return ref +} + +func get_remainder(poly uint64, deg uint, n uint) uint64 { + + rem, _ := xnmodp(n, poly, deg) + return rem +} + +func get_quotient(poly uint64, bits, n uint) uint64 { + + _, div := xnmodp(n, poly, bits) + return div +} + +// xnmodp returns two values, p and div: +// p is the representation of the binary polynomial x**n mod (x ** deg + "poly") +// That is p is the binary representation of the modulus polynomial except for its highest-order term. +// div is the binary representation of the polynomial x**n / (x ** deg + "poly") +func xnmodp(n uint, poly uint64, deg uint) (uint64, uint64) { + + var mod, mask, high, div uint64 + + if n < deg { + div = 0 + return poly, div + } + mask = 1<<deg - 1 + poly &= mask + mod = poly + div = 1 + deg-- + n-- + for n > deg { + high = (mod >> deg) & 1 + div = (div << 1) | high + mod <<= 1 + if high != 0 { + mod ^= poly + } + n-- + } + return mod & mask, div +} + +func main() { + w := new(bytes.Buffer) + + fmt.Fprintf(w, "// autogenerated: do not edit!\n") + fmt.Fprintf(w, "// generated from crc32/gen_const_ppc64le.go\n") + fmt.Fprintln(w) + fmt.Fprintf(w, "#include \"textflag.h\"\n") + + // These are the polynomials supported in vector now. + // If adding others, include the polynomial and a name + // to identify it. + + genCrc32ConstTable(w, 0xedb88320, "IEEE") + genCrc32ConstTable(w, 0x82f63b78, "Cast") + genCrc32ConstTable(w, 0xeb31d82e, "Koop") + b := w.Bytes() + + err := os.WriteFile("crc32_table_ppc64le.s", b, 0666) + if err != nil { + fmt.Printf("can't write output: %s\n", err) + } +} + +func genCrc32ConstTable(w *bytes.Buffer, poly uint32, polyid string) { + + ref_poly := reflect_bits(uint64(poly), 32) + fmt.Fprintf(w, "\n\t/* Reduce %d kbits to 1024 bits */\n", blocking*8) + j := 0 + for i := (blocking * 8) - 1024; i > 0; i -= 1024 { + a := reflect_bits(get_remainder(ref_poly, 32, uint(i)), 32) << 1 + b := reflect_bits(get_remainder(ref_poly, 32, uint(i+64)), 32) << 1 + + fmt.Fprintf(w, "\t/* x^%d mod p(x)%s, x^%d mod p(x)%s */\n", uint(i+64), "", uint(i), "") + fmt.Fprintf(w, "DATA ·%sConst+%d(SB)/8,$0x%016x\n", polyid, j*8, b) + fmt.Fprintf(w, "DATA ·%sConst+%d(SB)/8,$0x%016x\n", polyid, (j+1)*8, a) + + j += 2 + fmt.Fprintf(w, "\n") + } + + for i := (1024 * 2) - 128; i >= 0; i -= 128 { + a := reflect_bits(get_remainder(ref_poly, 32, uint(i+32)), 32) + b := reflect_bits(get_remainder(ref_poly, 32, uint(i+64)), 32) + c := reflect_bits(get_remainder(ref_poly, 32, uint(i+96)), 32) + d := reflect_bits(get_remainder(ref_poly, 32, uint(i+128)), 32) + + fmt.Fprintf(w, "\t/* x^%d mod p(x)%s, x^%d mod p(x)%s, x^%d mod p(x)%s, x^%d mod p(x)%s */\n", i+128, "", i+96, "", i+64, "", i+32, "") + fmt.Fprintf(w, "DATA ·%sConst+%d(SB)/8,$0x%08x%08x\n", polyid, j*8, c, d) + fmt.Fprintf(w, "DATA ·%sConst+%d(SB)/8,$0x%08x%08x\n", polyid, (j+1)*8, a, b) + + j += 2 + fmt.Fprintf(w, "\n") + } + + fmt.Fprintf(w, "GLOBL ·%sConst(SB),RODATA,$4336\n", polyid) + fmt.Fprintf(w, "\n /* Barrett constant m - (4^32)/n */\n") + fmt.Fprintf(w, "DATA ·%sBarConst(SB)/8,$0x%016x\n", polyid, reflect_bits(get_quotient(ref_poly, 32, 64), 33)) + fmt.Fprintf(w, "DATA ·%sBarConst+8(SB)/8,$0x0000000000000000\n", polyid) + fmt.Fprintf(w, "DATA ·%sBarConst+16(SB)/8,$0x%016x\n", polyid, reflect_bits((uint64(1)<<32)|ref_poly, 33)) // reflected? + fmt.Fprintf(w, "DATA ·%sBarConst+24(SB)/8,$0x0000000000000000\n", polyid) + fmt.Fprintf(w, "GLOBL ·%sBarConst(SB),RODATA,$32\n", polyid) +} |