lib/uzlib/defl_static: Implement some code size improvements.

This commit makes the following changes:
- Replace 256-byte reverse-bits-in-byte lookup table with computation.
- Replace length and distance code lookup tables with computation.
- Remove comp_disabled check (it's unused).
- Make the dest_write_cb take the data pointer directly, rather than the
  Outbuf.

Saves 500 bytes on PYBV11.

Signed-off-by: Jim Mussared <[email protected]>

Author: jimmo

lib/uzlib/defl_static.c

@@ -10,6 +10,9 @@ Delchev, Andreas Schultz, Jeroen Massar, Wez Furlong, Nicolas Barry,
 Justin Bradford, Ben Harris, Malcolm Smith, Ahmad Khalifa, Markus
 Kuhn, Colin Watson, and CORE SDI S.A.
 
+Optimised for MicroPython:
+Copyright (c) 2023 by Jim Mussared
+
 Permission is hereby granted, free of charge, to any person
 obtaining a copy of this software and associated documentation files
 (the "Software"), to deal in the Software without restriction,
@@ -55,152 +58,44 @@ static void outbits(struct Outbuf *out, unsigned long bits, int nbits)
     out->outbits |= bits << out->noutbits;
     out->noutbits += nbits;
     while (out->noutbits >= 8) {
-        out->dest_write_cb(out, out->outbits & 0xFF);
+        out->dest_write_cb(out->dest_write_data, out->outbits & 0xFF);
         out->outbits >>= 8;
         out->noutbits -= 8;
     }
 }
 
-static const unsigned char mirrorbytes[256] = {
-    0x00, 0x80, 0x40, 0xc0, 0x20, 0xa0, 0x60, 0xe0,
-    0x10, 0x90, 0x50, 0xd0, 0x30, 0xb0, 0x70, 0xf0,
-    0x08, 0x88, 0x48, 0xc8, 0x28, 0xa8, 0x68, 0xe8,
-    0x18, 0x98, 0x58, 0xd8, 0x38, 0xb8, 0x78, 0xf8,
-    0x04, 0x84, 0x44, 0xc4, 0x24, 0xa4, 0x64, 0xe4,
-    0x14, 0x94, 0x54, 0xd4, 0x34, 0xb4, 0x74, 0xf4,
-    0x0c, 0x8c, 0x4c, 0xcc, 0x2c, 0xac, 0x6c, 0xec,
-    0x1c, 0x9c, 0x5c, 0xdc, 0x3c, 0xbc, 0x7c, 0xfc,
-    0x02, 0x82, 0x42, 0xc2, 0x22, 0xa2, 0x62, 0xe2,
-    0x12, 0x92, 0x52, 0xd2, 0x32, 0xb2, 0x72, 0xf2,
-    0x0a, 0x8a, 0x4a, 0xca, 0x2a, 0xaa, 0x6a, 0xea,
-    0x1a, 0x9a, 0x5a, 0xda, 0x3a, 0xba, 0x7a, 0xfa,
-    0x06, 0x86, 0x46, 0xc6, 0x26, 0xa6, 0x66, 0xe6,
-    0x16, 0x96, 0x56, 0xd6, 0x36, 0xb6, 0x76, 0xf6,
-    0x0e, 0x8e, 0x4e, 0xce, 0x2e, 0xae, 0x6e, 0xee,
-    0x1e, 0x9e, 0x5e, 0xde, 0x3e, 0xbe, 0x7e, 0xfe,
-    0x01, 0x81, 0x41, 0xc1, 0x21, 0xa1, 0x61, 0xe1,
-    0x11, 0x91, 0x51, 0xd1, 0x31, 0xb1, 0x71, 0xf1,
-    0x09, 0x89, 0x49, 0xc9, 0x29, 0xa9, 0x69, 0xe9,
-    0x19, 0x99, 0x59, 0xd9, 0x39, 0xb9, 0x79, 0xf9,
-    0x05, 0x85, 0x45, 0xc5, 0x25, 0xa5, 0x65, 0xe5,
-    0x15, 0x95, 0x55, 0xd5, 0x35, 0xb5, 0x75, 0xf5,
-    0x0d, 0x8d, 0x4d, 0xcd, 0x2d, 0xad, 0x6d, 0xed,
-    0x1d, 0x9d, 0x5d, 0xdd, 0x3d, 0xbd, 0x7d, 0xfd,
-    0x03, 0x83, 0x43, 0xc3, 0x23, 0xa3, 0x63, 0xe3,
-    0x13, 0x93, 0x53, 0xd3, 0x33, 0xb3, 0x73, 0xf3,
-    0x0b, 0x8b, 0x4b, 0xcb, 0x2b, 0xab, 0x6b, 0xeb,
-    0x1b, 0x9b, 0x5b, 0xdb, 0x3b, 0xbb, 0x7b, 0xfb,
-    0x07, 0x87, 0x47, 0xc7, 0x27, 0xa7, 0x67, 0xe7,
-    0x17, 0x97, 0x57, 0xd7, 0x37, 0xb7, 0x77, 0xf7,
-    0x0f, 0x8f, 0x4f, 0xcf, 0x2f, 0xaf, 0x6f, 0xef,
-    0x1f, 0x9f, 0x5f, 0xdf, 0x3f, 0xbf, 0x7f, 0xff,
+static const unsigned char mirrornibbles[16] = {
+    0x0, 0x8, 0x4, 0xc, 0x2, 0xa, 0x6, 0xe,
+    0x1, 0x9, 0x5, 0xd, 0x3, 0xb, 0x7, 0xf,
 };
 
-typedef struct {
-    uint8_t extrabits;
-    uint8_t min, max;
-} len_coderecord;
-
-typedef struct {
-    uint8_t code, extrabits;
-    uint16_t min, max;
-} dist_coderecord;
-
-#define TO_LCODE(x, y) x - 3, y - 3
-#define FROM_LCODE(x) (x + 3)
-
-static const len_coderecord lencodes[] = {
-    {0, TO_LCODE(3, 3)},
-    {0, TO_LCODE(4, 4)},
-    {0, TO_LCODE(5, 5)},
-    {0, TO_LCODE(6, 6)},
-    {0, TO_LCODE(7, 7)},
-    {0, TO_LCODE(8, 8)},
-    {0, TO_LCODE(9, 9)},
-    {0, TO_LCODE(10, 10)},
-    {1, TO_LCODE(11, 12)},
-    {1, TO_LCODE(13, 14)},
-    {1, TO_LCODE(15, 16)},
-    {1, TO_LCODE(17, 18)},
-    {2, TO_LCODE(19, 22)},
-    {2, TO_LCODE(23, 26)},
-    {2, TO_LCODE(27, 30)},
-    {2, TO_LCODE(31, 34)},
-    {3, TO_LCODE(35, 42)},
-    {3, TO_LCODE(43, 50)},
-    {3, TO_LCODE(51, 58)},
-    {3, TO_LCODE(59, 66)},
-    {4, TO_LCODE(67, 82)},
-    {4, TO_LCODE(83, 98)},
-    {4, TO_LCODE(99, 114)},
-    {4, TO_LCODE(115, 130)},
-    {5, TO_LCODE(131, 162)},
-    {5, TO_LCODE(163, 194)},
-    {5, TO_LCODE(195, 226)},
-    {5, TO_LCODE(227, 257)},
-    {0, TO_LCODE(258, 258)},
-};
+static unsigned int mirrorbyte(unsigned int b) {
+    return mirrornibbles[b & 0xf] << 4 | mirrornibbles[b >> 4];
+}
 
-static const dist_coderecord distcodes[] = {
-    {0, 0, 1, 1},
-    {1, 0, 2, 2},
-    {2, 0, 3, 3},
-    {3, 0, 4, 4},
-    {4, 1, 5, 6},
-    {5, 1, 7, 8},
-    {6, 2, 9, 12},
-    {7, 2, 13, 16},
-    {8, 3, 17, 24},
-    {9, 3, 25, 32},
-    {10, 4, 33, 48},
-    {11, 4, 49, 64},
-    {12, 5, 65, 96},
-    {13, 5, 97, 128},
-    {14, 6, 129, 192},
-    {15, 6, 193, 256},
-    {16, 7, 257, 384},
-    {17, 7, 385, 512},
-    {18, 8, 513, 768},
-    {19, 8, 769, 1024},
-    {20, 9, 1025, 1536},
-    {21, 9, 1537, 2048},
-    {22, 10, 2049, 3072},
-    {23, 10, 3073, 4096},
-    {24, 11, 4097, 6144},
-    {25, 11, 6145, 8192},
-    {26, 12, 8193, 12288},
-    {27, 12, 12289, 16384},
-    {28, 13, 16385, 24576},
-    {29, 13, 24577, 32768},
-};
+static int int_log2(int x) {
+    int r = 0;
+    while (x >>= 1) {
+        ++r;
+    }
+    return r;
+}
 
 void zlib_literal(struct Outbuf *out, unsigned char c)
 {
-    if (out->comp_disabled) {
-        /*
-         * We're in an uncompressed block, so just output the byte.
-         */
-        outbits(out, c, 8);
-        return;
-    }
-
     if (c <= 143) {
         /* 0 through 143 are 8 bits long starting at 00110000. */
-        outbits(out, mirrorbytes[0x30 + c], 8);
+        outbits(out, mirrorbyte(0x30 + c), 8);
     } else {
         /* 144 through 255 are 9 bits long starting at 110010000. */
-        outbits(out, 1 + 2 * mirrorbytes[0x90 - 144 + c], 9);
+        outbits(out, 1 + 2 * mirrorbyte(0x90 - 144 + c), 9);
     }
 }
 
 void zlib_match(struct Outbuf *out, int distance, int len)
 {
-    const dist_coderecord *d;
-    const len_coderecord *l;
-    int i, j, k;
-    int lcode;
-
-    assert(!out->comp_disabled);
+    assert(distance >= 1 && distance <= 32768);
+    distance -= 1;
 
     while (len > 0) {
         int thislen;
@@ -218,73 +113,56 @@ void zlib_match(struct Outbuf *out, int distance, int len)
         thislen = (len > 260 ? 258 : len <= 258 ? len : len - 3);
         len -= thislen;
 
-        /*
-         * Binary-search to find which length code we're
-         * transmitting.
-         */
-        i = -1;
-        j = sizeof(lencodes) / sizeof(*lencodes);
-        while (1) {
-            assert(j - i >= 2);
-            k = (j + i) / 2;
-            if (thislen < FROM_LCODE(lencodes[k].min))
-                j = k;
-            else if (thislen > FROM_LCODE(lencodes[k].max))
-                i = k;
-            else {
-                l = &lencodes[k];
-                break;                 /* found it! */
+        assert(thislen >= 3 && thislen <= 258);
+
+        thislen -= 3;
+        int lcode = 28;
+        int x = int_log2(thislen);
+        int y;
+        if (thislen < 255) {
+            if (x) {
+                --x;
             }
+            y = (thislen >> (x ? x - 1 : 0)) & 3;
+            lcode = x * 4 + y;
         }
 
-        lcode = l - lencodes + 257;
-
         /*
          * Transmit the length code. 256-279 are seven bits
          * starting at 0000000; 280-287 are eight bits starting at
          * 11000000.
          */
-        if (lcode <= 279) {
-            outbits(out, mirrorbytes[(lcode - 256) * 2], 7);
+        if (lcode <= 22) {
+            outbits(out, mirrorbyte((lcode + 1) * 2), 7);
         } else {
-            outbits(out, mirrorbytes[0xc0 - 280 + lcode], 8);
+            outbits(out, mirrorbyte(lcode + 169), 8);
         }
 
         /*
          * Transmit the extra bits.
          */
-        if (l->extrabits)
-            outbits(out, thislen - FROM_LCODE(l->min), l->extrabits);
-
-        /*
-         * Binary-search to find which distance code we're
-         * transmitting.
-         */
-        i = -1;
-        j = sizeof(distcodes) / sizeof(*distcodes);
-        while (1) {
-            assert(j - i >= 2);
-            k = (j + i) / 2;
-            if (distance < distcodes[k].min)
-                j = k;
-            else if (distance > distcodes[k].max)
-                i = k;
-            else {
-                d = &distcodes[k];
-                break;                 /* found it! */
-            }
+        if (thislen < 255 && x > 1) {
+            int extrabits = x - 1;
+            int lmin = (thislen >> extrabits) << extrabits;
+            outbits(out, thislen - lmin, extrabits);
         }
 
+        x = int_log2(distance);
+        y = (distance >> (x ? x - 1 : 0)) & 1;
+
         /*
          * Transmit the distance code. Five bits starting at 00000.
          */
-        outbits(out, mirrorbytes[d->code * 8], 5);
+        outbits(out, mirrorbyte((x * 2 + y) * 8), 5);
 
         /*
          * Transmit the extra bits.
          */
-        if (d->extrabits)
-            outbits(out, distance - d->min, d->extrabits);
+        if (x > 1) {
+            int dextrabits = x - 1;
+            int dmin = (distance >> dextrabits) << dextrabits;
+            outbits(out, distance - dmin, dextrabits);
+        }
     }
 }
 

lib/uzlib/defl_static.h

@@ -32,10 +32,9 @@
 
 struct Outbuf {
     void *dest_write_data;
-    void (*dest_write_cb)(struct Outbuf *outbuf, uint8_t byte);
+    void (*dest_write_cb)(void *data, uint8_t byte);
     unsigned long outbits;
     int noutbits;
-    int comp_disabled;
 };
 
 void zlib_start_block(struct Outbuf *ctx);