Initial import

libc/str/tpdecodecb.h

@@ -0,0 +1,56 @@
+/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
+│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 2020 Justine Alexandra Roberts Tunney                              │
+│                                                                              │
+│ This program 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; version 2 of the License.                      │
+│                                                                              │
+│ This program 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.                                     │
+│                                                                              │
+│ You should have received a copy of the GNU General Public License            │
+│ along with this program; if not, write to the Free Software                  │
+│ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA                │
+│ 02110-1301 USA                                                               │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#ifndef COSMOPOLITAN_LIBC_STR_TPDECODECB_H_
+#define COSMOPOLITAN_LIBC_STR_TPDECODECB_H_
+#if !(__ASSEMBLER__ + __LINKER__ + 0)
+
+/**
+ * Generic Thompson-Pike Varint Decoder.
+ * @return number of bytes successfully consumed or -1 w/ errno
+ * @note synchronization is performed
+ */
+forceinline int tpdecodecb(wint_t *out, int first,
+                           int get(void *arg, uint32_t i), void *arg) {
+  uint32_t wc, cb, need, msb, i = 1;
+  if ((wc = first) == -1) return -1;
+  while ((wc & 0b11000000) == 0b10000000) {
+    if ((wc = get(arg, i++)) == -1) return -1;
+  }
+  if ((wc & 0b10000000) == 0b10000000) {
+    asm("bsr\t%1,%0" : "=r"(msb) : "rm"(~wc & 0xff) : "cc");
+    if (!msb) msb = 1;
+    need = 7 - msb;
+    wc &= ((1u << msb) - 1) | 0b00000011;
+    for (uint32_t j = 1; j < need; ++j) {
+      if ((cb = get(arg, i++)) == -1) return -1;
+      if ((cb & 0b11000000) == 0b10000000) {
+        wc = wc << 6 | (cb & 0b00111111);
+      } else {
+        if (out) *out = u'<EFBFBD>';
+        return -1;
+      }
+    }
+  }
+  if (out) *out = (wint_t)wc;
+  return i;
+}
+
+#endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */
+#endif /* COSMOPOLITAN_LIBC_STR_TPDECODECB_H_ */