1 // SPDX-License-Identifier: GPL-2.0 2 #include <linux/bitops.h> 3 #include <linux/bug.h> 4 #include <linux/export.h> 5 #include <linux/limits.h> 6 #include <linux/math.h> 7 #include <linux/minmax.h> 8 #include <linux/types.h> 9 10 #include <linux/reciprocal_div.h> 11 12 /* 13 * For a description of the algorithm please have a look at 14 * include/linux/reciprocal_div.h 15 */ 16 17 struct reciprocal_value reciprocal_value(u32 d) 18 { 19 struct reciprocal_value R; 20 u64 m; 21 int l; 22 23 l = fls(d - 1); 24 m = ((1ULL << 32) * ((1ULL << l) - d)); 25 do_div(m, d); 26 ++m; 27 R.m = (u32)m; 28 R.sh1 = min(l, 1); 29 R.sh2 = max(l - 1, 0); 30 31 return R; 32 } 33 EXPORT_SYMBOL(reciprocal_value); 34 35 struct reciprocal_value_adv reciprocal_value_adv(u32 d, u8 prec) 36 { 37 struct reciprocal_value_adv R; 38 u32 l, post_shift; 39 u64 mhigh, mlow; 40 41 /* ceil(log2(d)) */ 42 l = fls(d - 1); 43 /* NOTE: mlow/mhigh could overflow u64 when l == 32. This case needs to 44 * be handled before calling "reciprocal_value_adv", please see the 45 * comment at include/linux/reciprocal_div.h. 46 */ 47 WARN(l == 32, 48 "ceil(log2(0x%08x)) == 32, %s doesn't support such divisor", 49 d, __func__); 50 post_shift = l; 51 mlow = 1ULL << (32 + l); 52 do_div(mlow, d); 53 mhigh = (1ULL << (32 + l)) + (1ULL << (32 + l - prec)); 54 do_div(mhigh, d); 55 56 for (; post_shift > 0; post_shift--) { 57 u64 lo = mlow >> 1, hi = mhigh >> 1; 58 59 if (lo >= hi) 60 break; 61 62 mlow = lo; 63 mhigh = hi; 64 } 65 66 R.m = (u32)mhigh; 67 R.sh = post_shift; 68 R.exp = l; 69 R.is_wide_m = mhigh > U32_MAX; 70 71 return R; 72 } 73 EXPORT_SYMBOL(reciprocal_value_adv); 74