lib/builtins/udivmoddi4.c

//===-- udivmoddi4.c - Implement __udivmoddi4 -----------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file implements __udivmoddi4 for the compiler_rt library.
//
//===----------------------------------------------------------------------===//

#include "int_lib.h"

// Effects: if rem != 0, *rem = a % b
// Returns: a / b

// Translated from Figure 3-40 of The PowerPC Compiler Writer's Guide

COMPILER_RT_ABI du_int __udivmoddi4(du_int a, du_int b, du_int *rem) {
  const unsigned n_uword_bits = sizeof(su_int) * CHAR_BIT;
  const unsigned n_udword_bits = sizeof(du_int) * CHAR_BIT;
  udwords n;
  n.all = a;
  udwords d;
  d.all = b;
  udwords q;
  udwords r;
  unsigned sr;
  // special cases, X is unknown, K != 0
  if (n.s.high == 0) {
    if (d.s.high == 0) {
      // 0 X
      // ---
      // 0 X
      if (rem)
        *rem = n.s.low % d.s.low;
      return n.s.low / d.s.low;
    }
    // 0 X
    // ---
    // K X
    if (rem)
      *rem = n.s.low;
    return 0;
  }
  // n.s.high != 0
  if (d.s.low == 0) {
    if (d.s.high == 0) {
      // K X
      // ---
      // 0 0
      if (rem)
        *rem = n.s.high % d.s.low;
      return n.s.high / d.s.low;
    }
    // d.s.high != 0
    if (n.s.low == 0) {
      // K 0
      // ---
      // K 0
      if (rem) {
        r.s.high = n.s.high % d.s.high;
        r.s.low = 0;
        *rem = r.all;
      }
      return n.s.high / d.s.high;
    }
    // K K
    // ---
    // K 0
    if ((d.s.high & (d.s.high - 1)) == 0) /* if d is a power of 2 */ {
      if (rem) {
        r.s.low = n.s.low;
        r.s.high = n.s.high & (d.s.high - 1);
        *rem = r.all;
      }
      return n.s.high >> __builtin_ctz(d.s.high);
    }
    // K K
    // ---
    // K 0
    sr = __builtin_clz(d.s.high) - __builtin_clz(n.s.high);
    // 0 <= sr <= n_uword_bits - 2 or sr large
    if (sr > n_uword_bits - 2) {
      if (rem)
        *rem = n.all;
      return 0;
    }
    ++sr;
    // 1 <= sr <= n_uword_bits - 1
    // q.all = n.all << (n_udword_bits - sr);
    q.s.low = 0;
    q.s.high = n.s.low << (n_uword_bits - sr);
    // r.all = n.all >> sr;
    r.s.high = n.s.high >> sr;
    r.s.low = (n.s.high << (n_uword_bits - sr)) | (n.s.low >> sr);
  } else /* d.s.low != 0 */ {
    if (d.s.high == 0) {
      // K X
      // ---
      // 0 K
      if ((d.s.low & (d.s.low - 1)) == 0) /* if d is a power of 2 */ {
        if (rem)
          *rem = n.s.low & (d.s.low - 1);
        if (d.s.low == 1)
          return n.all;
        sr = __builtin_ctz(d.s.low);
        q.s.high = n.s.high >> sr;
        q.s.low = (n.s.high << (n_uword_bits - sr)) | (n.s.low >> sr);
        return q.all;
      }
      // K X
      // ---
      // 0 K
      sr = 1 + n_uword_bits + __builtin_clz(d.s.low) - __builtin_clz(n.s.high);
      // 2 <= sr <= n_udword_bits - 1
      // q.all = n.all << (n_udword_bits - sr);
      // r.all = n.all >> sr;
      if (sr == n_uword_bits) {
        q.s.low = 0;
        q.s.high = n.s.low;
        r.s.high = 0;
        r.s.low = n.s.high;
      } else if (sr < n_uword_bits) /* 2 <= sr <= n_uword_bits - 1 */ {
        q.s.low = 0;
        q.s.high = n.s.low << (n_uword_bits - sr);
        r.s.high = n.s.high >> sr;
        r.s.low = (n.s.high << (n_uword_bits - sr)) | (n.s.low >> sr);
      } else /* n_uword_bits + 1 <= sr <= n_udword_bits - 1 */ {
        q.s.low = n.s.low << (n_udword_bits - sr);
        q.s.high = (n.s.high << (n_udword_bits - sr)) |
                   (n.s.low >> (sr - n_uword_bits));
        r.s.high = 0;
        r.s.low = n.s.high >> (sr - n_uword_bits);
      }
    } else {
      // K X
      // ---
      // K K
      sr = __builtin_clz(d.s.high) - __builtin_clz(n.s.high);
      // 0 <= sr <= n_uword_bits - 1 or sr large
      if (sr > n_uword_bits - 1) {
        if (rem)
          *rem = n.all;
        return 0;
      }
      ++sr;
      // 1 <= sr <= n_uword_bits
      // q.all = n.all << (n_udword_bits - sr);
      q.s.low = 0;
      if (sr == n_uword_bits) {
        q.s.high = n.s.low;
        r.s.high = 0;
        r.s.low = n.s.high;
      } else {
        q.s.high = n.s.low << (n_uword_bits - sr);
        r.s.high = n.s.high >> sr;
        r.s.low = (n.s.high << (n_uword_bits - sr)) | (n.s.low >> sr);
      }
    }
  }
  // Not a special case
  // q and r are initialized with:
  // q.all = n.all << (n_udword_bits - sr);
  // r.all = n.all >> sr;
  // 1 <= sr <= n_udword_bits - 1
  su_int carry = 0;
  for (; sr > 0; --sr) {
    // r:q = ((r:q)  << 1) | carry
    r.s.high = (r.s.high << 1) | (r.s.low >> (n_uword_bits - 1));
    r.s.low = (r.s.low << 1) | (q.s.high >> (n_uword_bits - 1));
    q.s.high = (q.s.high << 1) | (q.s.low >> (n_uword_bits - 1));
    q.s.low = (q.s.low << 1) | carry;
    // carry = 0;
    // if (r.all >= d.all)
    // {
    //      r.all -= d.all;
    //      carry = 1;
    // }
    const di_int s = (di_int)(d.all - r.all - 1) >> (n_udword_bits - 1);
    carry = s & 1;
    r.all -= d.all & s;
  }
  q.all = (q.all << 1) | carry;
  if (rem)
    *rem = r.all;
  return q.all;
}