upb/mini_descriptor/internal/base92.h

// Protocol Buffers - Google's data interchange format
// Copyright 2023 Google LLC.  All rights reserved.
//
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file or at
// https://developers.google.com/open-source/licenses/bsd

#ifndef UPB_MINI_DESCRIPTOR_INTERNAL_BASE92_H_
#define UPB_MINI_DESCRIPTOR_INTERNAL_BASE92_H_

#include <stdint.h>

#include "upb/base/internal/log2.h"

// Must be last.
#include "upb/port/def.inc"

#ifdef __cplusplus
extern "C" {
#endif

UPB_INLINE char _upb_ToBase92(int8_t ch) {
  extern const char _kUpb_ToBase92[];
  UPB_ASSERT(0 <= ch && ch < 92);
  return _kUpb_ToBase92[ch];
}

UPB_INLINE char _upb_FromBase92(uint8_t ch) {
  extern const int8_t _kUpb_FromBase92[];
  if (' ' > ch || ch > '~') return -1;
  return _kUpb_FromBase92[ch - ' '];
}

UPB_INLINE const char* _upb_Base92_DecodeVarint(const char* ptr,
                                                const char* end, char first_ch,
                                                uint8_t min, uint8_t max,
                                                uint32_t* out_val) {
  uint32_t val = 0;
  uint32_t shift = 0;
  const int bits_per_char =
      upb_Log2Ceiling(_upb_FromBase92(max) - _upb_FromBase92(min));
  char ch = first_ch;
  while (1) {
    uint32_t bits = _upb_FromBase92(ch) - _upb_FromBase92(min);
    val |= bits << shift;
    if (ptr == end || *ptr < min || max < *ptr) {
      *out_val = val;
      UPB_ASSUME(ptr != NULL);
      return ptr;
    }
    ch = *ptr++;
    shift += bits_per_char;
    if (shift >= 32) return NULL;
  }
}

#ifdef __cplusplus
} /* extern "C" */
#endif

#include "upb/port/undef.inc"

#endif  // UPB_MINI_DESCRIPTOR_INTERNAL_BASE92_H_