1 // SPDX-License-Identifier: GPL-2.0 2 #include <linux/bug.h> 3 #include <linux/kernel.h> 4 #include <asm/div64.h> 5 #include <linux/reciprocal_div.h> 6 #include <linux/export.h> 7 #include <linux/minmax.h> 8 9 /* 10 * For a description of the algorithm please have a look at 11 * include/linux/reciprocal_div.h 12 */ 13 14 struct reciprocal_value reciprocal_value(u32 d) 15 { 16 struct reciprocal_value R; 17 u64 m; 18 int l; 19 20 l = fls(d - 1); 21 m = ((1ULL << 32) * ((1ULL << l) - d)); 22 do_div(m, d); 23 ++m; 24 R.m = (u32)m; 25 R.sh1 = min(l, 1); 26 R.sh2 = max(l - 1, 0); 27 28 return R; 29 } 30 EXPORT_SYMBOL(reciprocal_value); 31 32 struct reciprocal_value_adv reciprocal_value_adv(u32 d, u8 prec) 33 { 34 struct reciprocal_value_adv R; 35 u32 l, post_shift; 36 u64 mhigh, mlow; 37 38 /* ceil(log2(d)) */ 39 l = fls(d - 1); 40 /* NOTE: mlow/mhigh could overflow u64 when l == 32. This case needs to 41 * be handled before calling "reciprocal_value_adv", please see the 42 * comment at include/linux/reciprocal_div.h. 43 */ 44 WARN(l == 32, 45 "ceil(log2(0x%08x)) == 32, %s doesn't support such divisor", 46 d, __func__); 47 post_shift = l; 48 mlow = 1ULL << (32 + l); 49 do_div(mlow, d); 50 mhigh = (1ULL << (32 + l)) + (1ULL << (32 + l - prec)); 51 do_div(mhigh, d); 52 53 for (; post_shift > 0; post_shift--) { 54 u64 lo = mlow >> 1, hi = mhigh >> 1; 55 56 if (lo >= hi) 57 break; 58 59 mlow = lo; 60 mhigh = hi; 61 } 62 63 R.m = (u32)mhigh; 64 R.sh = post_shift; 65 R.exp = l; 66 R.is_wide_m = mhigh > U32_MAX; 67 68 return R; 69 } 70 EXPORT_SYMBOL(reciprocal_value_adv); 71