zlib: inflate using wider loads and stores

third_party/zlib/contrib/arm/chunkcopy.h

+/* chunkcopy.h -- fast copies and sets
+ * Copyright (C) 2017 ARM, Inc.
+ * For conditions of distribution and use, see copyright notice in zlib.h
+ */
+
+#ifndef CHUNKCOPY_H
+#define CHUNKCOPY_H
+
+#include "zutil.h"
+#include <arm_neon.h>
+
+#if __STDC_VERSION__ >= 199901L
+#define Z_RESTRICT restrict
+#else
+#define Z_RESTRICT
+#endif
+
+typedef uint8x16_t chunkcopy_chunk_t;
+#define CHUNKCOPY_CHUNK_SIZE sizeof(chunkcopy_chunk_t)
+
+/*
+   Ask the compiler to perform a wide, unaligned load with an machine
+   instruction appropriate for the chunkcopy_chunk_t type.
+ */
+static inline chunkcopy_chunk_t loadchunk(const unsigned char FAR *s) {
+    chunkcopy_chunk_t c;
+    __builtin_memcpy(&c, s, sizeof(c));
+    return c;
+}
+
+/*
+   Ask the compiler to perform a wide, unaligned store with an machine
+   instruction appropriate for the chunkcopy_chunk_t type.
+ */
+static inline void storechunk(unsigned char FAR *d, chunkcopy_chunk_t c) {
+    __builtin_memcpy(d, &c, sizeof(c));
+}
+
+/*
+   Perform a memcpy-like operation, but assume that length is non-zero and that
+   it's OK to overwrite at least CHUNKCOPY_CHUNK_SIZE bytes of output even if
+   the length is shorter than this.
+
+   It also guarantees that it will properly unroll the data if the distance
+   between `out` and `from` is at least CHUNKCOPY_CHUNK_SIZE, which we rely on
+   in chunkcopy_relaxed().
+
+   Aside from better memory bus utilisation, this means that short copies
+   (CHUNKCOPY_CHUNK_SIZE bytes or fewer) will fall straight through the loop
+   without iteration, which will hopefully make the branch prediction more
+   reliable.
+ */
+static inline unsigned char FAR *chunkcopy_core(unsigned char FAR *out,
+                                                const unsigned char FAR *from,
+                                                unsigned len) {
+    int bump = (--len % CHUNKCOPY_CHUNK_SIZE) + 1;
+    storechunk(out, loadchunk(from));
+    out += bump;
+    from += bump;
+    len /= CHUNKCOPY_CHUNK_SIZE;
+    while (len-- > 0) {
+        storechunk(out, loadchunk(from));
+        out += CHUNKCOPY_CHUNK_SIZE;
+        from += CHUNKCOPY_CHUNK_SIZE;
+    }
+    return out;
+}
+
+/*
+   Like chunkcopy_core, but avoid writing beyond of legal output.
+
+   Accepts an additional pointer to the end of safe output.  A generic safe
+   copy would use (out + len), but it's normally the case that the end of the
+   output buffer is beyond the end of the current copy, and this can still be
+   exploited.
+ */
+static inline unsigned char FAR *chunkcopy_core_safe(unsigned char FAR *out,
+                                                     const unsigned char FAR * from,
+                                                     unsigned len,
+                                                     unsigned char FAR *limit) {
+    Assert(out + len <= limit, "chunk copy exceeds safety limit");
+    if (limit - out < CHUNKCOPY_CHUNK_SIZE) {
+        const unsigned char FAR * Z_RESTRICT rfrom = from;
+        if (len & 8) { __builtin_memcpy(out, rfrom, 8); out += 8; rfrom += 8; }
+        if (len & 4) { __builtin_memcpy(out, rfrom, 4); out += 4; rfrom += 4; }
+        if (len & 2) { __builtin_memcpy(out, rfrom, 2); out += 2; rfrom += 2; }
+        if (len & 1) { *out++ = *rfrom++; }
+        return out;
+    }
+    return chunkcopy_core(out, from, len);
+}
+
+/*
+   Perform short copies until distance can be rewritten as being at least
+   CHUNKCOPY_CHUNK_SIZE.
+
+   This assumes that it's OK to overwrite at least the first
+   2*CHUNKCOPY_CHUNK_SIZE bytes of output even if the copy is shorter than
+   this.  This assumption holds within inflate_fast() which starts every
+   iteration with at least 258 bytes of output space available (258 being the
+   maximum length output from a single token; see inffast.c).
+ */
+static inline unsigned char FAR *chunkunroll_relaxed(unsigned char FAR *out,
+                                                     unsigned FAR *dist,
+                                                     unsigned FAR *len) {
+    const unsigned char FAR *from = out - *dist;
+    while (*dist < *len && *dist < CHUNKCOPY_CHUNK_SIZE) {
+        storechunk(out, loadchunk(from));
+        out += *dist;
+        *len -= *dist;
+        *dist += *dist;
+    }
+    return out;
+}
+
+
+static inline uint8x16_t chunkset_vld1q_dup_u8x8(const unsigned char FAR * Z_RESTRICT from) {
+#if defined(__clang__) || defined(__aarch64__)
+    return vreinterpretq_u8_u64(vld1q_dup_u64((void *)from));
+#else
+    /* 32-bit GCC uses an alignment hint for vld1q_dup_u64, even when given a
+     * void pointer, so here's an alternate implementation.
+     */
+    uint8x8_t h = vld1_u8(from);
+    return vcombine_u8(h, h);
+#endif
+}
+
+/*
+   Perform an overlapping copy which behaves as a memset() operation, but
+   supporting periods other than one, and assume that length is non-zero and
+   that it's OK to overwrite at least CHUNKCOPY_CHUNK_SIZE*3 bytes of output
+   even if the length is shorter than this.
+ */
+static inline unsigned char FAR *chunkset_core(unsigned char FAR *out,
+                                               unsigned period,
+                                               unsigned len) {
+    uint8x16_t f;
+    int bump = ((len - 1) % sizeof(f)) + 1;
+
+    switch (period) {
+    case 1:
+        f = vld1q_dup_u8(out - 1);
+        vst1q_u8(out, f);
+        out += bump;
+        len -= bump;
+        while (len > 0) {
+            vst1q_u8(out, f);
+            out += sizeof(f);
+            len -= sizeof(f);
+        }
+        return out;
+    case 2:
+        f = vreinterpretq_u8_u16(vld1q_dup_u16((void *)(out - 2)));
+        vst1q_u8(out, f);
+        out += bump;
+        len -= bump;
+        if (len > 0) {
+            f = vreinterpretq_u8_u16(vld1q_dup_u16((void *)(out - 2)));
+            do {
+                vst1q_u8(out, f);
+                out += sizeof(f);
+                len -= sizeof(f);
+            } while (len > 0);
+        }
+        return out;
+    case 4:
+        f = vreinterpretq_u8_u32(vld1q_dup_u32((void *)(out - 4)));
+        vst1q_u8(out, f);
+        out += bump;
+        len -= bump;
+        if (len > 0) {
+            f = vreinterpretq_u8_u32(vld1q_dup_u32((void *)(out - 4)));
+            do {
+                vst1q_u8(out, f);
+                out += sizeof(f);
+                len -= sizeof(f);
+            } while (len > 0);
+        }
+        return out;
+    case 8:
+        f = chunkset_vld1q_dup_u8x8(out - 8);
+        vst1q_u8(out, f);
+        out += bump;
+        len -= bump;
+        if (len > 0) {
+            f = chunkset_vld1q_dup_u8x8(out - 8);
+            do {
+                vst1q_u8(out, f);
+                out += sizeof(f);
+                len -= sizeof(f);
+            } while (len > 0);
+        }
+        return out;
+    }
+    out = chunkunroll_relaxed(out, &period, &len);
+    return chunkcopy_core(out, out - period, len);
+}
+
+/*
+   Perform a memcpy-like operation, but assume that length is non-zero and that
+   it's OK to overwrite at least CHUNKCOPY_CHUNK_SIZE bytes of output even if
+   the length is shorter than this.
+
+   Unlike chunkcopy_core() above, no guarantee is made regarding the behaviour
+   of overlapping buffers, regardless of the distance between the pointers.
+   This is reflected in the `restrict`-qualified pointers, allowing the
+   compiler to reorder loads and stores.
+ */
+static inline unsigned char FAR *chunkcopy_relaxed(unsigned char FAR * Z_RESTRICT out,
+                                                   const unsigned char FAR * Z_RESTRICT from,
+                                                   unsigned len) {
+    return chunkcopy_core(out, from, len);
+}
+
+/*
+   Like chunkcopy_relaxed, but avoid writing beyond of legal output.
+
+   Unlike chunkcopy_core_safe() above, no guarantee is made regarding the
+   behaviour of overlapping buffers, regardless of the distance between the
+   pointers.  This is reflected in the `restrict`-qualified pointers, allowing
+   the compiler to reorder loads and stores.
+
+   Accepts an additional pointer to the end of safe output.  A generic safe
+   copy would use (out + len), but it's normally the case that the end of the
+   output buffer is beyond the end of the current copy, and this can still be
+   exploited.
+ */
+static inline unsigned char FAR *chunkcopy_safe(unsigned char FAR *out,
+                                                const unsigned char FAR * Z_RESTRICT from,
+                                                unsigned len,
+                                                unsigned char FAR *limit) {
+    Assert(out + len <= limit, "chunk copy exceeds safety limit");
+    return chunkcopy_core_safe(out, from, len, limit);
+}
+
+/*
+   Perform chunky copy within the same buffer, where the source and destination
+   may potentially overlap.
+
+   Assumes that len > 0 on entry, and that it's safe to write at least
+   CHUNKCOPY_CHUNK_SIZE*3 bytes to the output.
+ */
+static inline unsigned char FAR *chunkcopy_lapped_relaxed(unsigned char FAR *out,
+                                                          unsigned dist,
+                                                          unsigned len) {
+    if (dist < len && dist < CHUNKCOPY_CHUNK_SIZE) {
+        return chunkset_core(out, dist, len);
+    }
+    return chunkcopy_core(out, out - dist, len);
+}
+
+/*
+   Behave like chunkcopy_lapped_relaxed, but avoid writing beyond of legal output.
+
+   Accepts an additional pointer to the end of safe output.  A generic safe
+   copy would use (out + len), but it's normally the case that the end of the
+   output buffer is beyond the end of the current copy, and this can still be
+   exploited.
+ */
+static inline unsigned char FAR *chunkcopy_lapped_safe(unsigned char FAR *out,
+                                                       unsigned dist,
+                                                       unsigned len,
+                                                       unsigned char FAR *limit) {
+    Assert(out + len <= limit, "chunk copy exceeds safety limit");
+    if (limit - out < CHUNKCOPY_CHUNK_SIZE * 3) {
+        /* TODO: try harder to optimise this */
+        while (len-- > 0) {
+            *out = *(out - dist);
+            out++;
+        }
+        return out;
+    }
+    return chunkcopy_lapped_relaxed(out, dist, len);
+}
+
+#undef Z_RESTRICT
+
+#endif /* CHUNKCOPY_H */