Initial import

libc/str/varint.h

@@ -0,0 +1,87 @@
+#ifndef COSMOPOLITAN_LIBC_VARINT_H_
+#define COSMOPOLITAN_LIBC_VARINT_H_
+#include "libc/limits.h"
+#if !(__ASSEMBLER__ + __LINKER__ + 0)
+
+#define unzigzag(x) ((x >> 1) ^ -(x & 1))
+#define zigzag(x)   _Generic((x), int32_t : zigzag32, default : zigzag64)(x)
+
+forceinline int32_t zigzag32(int32_t x) {
+  return (int64_t)((uint64_t)x << 1) ^ (x >> 31);
+}
+
+forceinline int64_t zigzag64(int64_t x) {
+  return (int64_t)((uint64_t)x << 1) ^ (x >> 63);
+}
+
+/**
+ * Copies variable-length integer to buffer.
+ *
+ * @param p needs 10+ bytes for 64-bit and 5+ for 32-bit
+ * @param x is unsigned number to encode
+ * @return pointer past last written byte
+ * @see writesint() which has more efficient encoding for signed numbers
+ */
+forceinline uint8_t *writevint(uint8_t *p, uint64_t x) {
+  do {
+    *p++ = (uint8_t)(x | 0x80);
+    x >>= 7;
+  } while (x > 0);
+  p[-1] &= 0x7f;
+  return p;
+}
+
+/**
+ * Copies variable-length signed integer to buffer.
+ *
+ * @param p needs 10+ bytes for 64-bit and 5+ for 32-bit
+ * @param x is unsigned number to encode
+ * @return pointer past last written byte
+ */
+forceinline uint8_t *writesint(uint8_t *p, int64_t x) {
+  return writevint(p, zigzag(x));
+}
+
+/**
+ * Reads variable-length integer from buffer.
+ *
+ * @param x is unsigned number to encode
+ * @return pointer past last read byte or -1ul on error
+ */
+forceinline uint8_t *readvint(uint8_t *p, uint8_t *pe, uint64_t *res) {
+  uint8_t b;
+  uint64_t x, o;
+  x = 0;
+  b = 0;
+  while (p < pe) {
+    o = *p++;
+    x |= ((uint64_t)o & 0x7f) << b;
+    if (!(o & 0x80)) {
+      *res = x;
+      return p;
+    }
+    if ((b += 7) > 64) {
+      break;
+    }
+  }
+  return (uint8_t *)-1ul;
+}
+
+/**
+ * Reads variable-length zig-zagged integer from buffer.
+ *
+ * @param x is unsigned number to encode
+ * @return pointer past last read byte or -1ul on error
+ */
+forceinline uint8_t *readsint(uint8_t *p, uint8_t *pe, int64_t *res) {
+  uint64_t u;
+  if ((p = readvint(p, pe, &u)) != (uint8_t *)-1ul) {
+    *res = unzigzag((int64_t)u);
+    return p;
+  } else {
+    return (uint8_t *)-1ul;
+  }
+}
+
+#endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */
+#endif /* COSMOPOLITAN_LIBC_VARINT_H_ */