Kyle Swenson | 8d8f654 | 2021-03-15 11:02:55 -0600 | [diff] [blame^] | 1 | #ifndef __ASM_ARM_DIV64 |
| 2 | #define __ASM_ARM_DIV64 |
| 3 | |
| 4 | #include <linux/types.h> |
| 5 | #include <asm/compiler.h> |
| 6 | |
| 7 | /* |
| 8 | * The semantics of do_div() are: |
| 9 | * |
| 10 | * uint32_t do_div(uint64_t *n, uint32_t base) |
| 11 | * { |
| 12 | * uint32_t remainder = *n % base; |
| 13 | * *n = *n / base; |
| 14 | * return remainder; |
| 15 | * } |
| 16 | * |
| 17 | * In other words, a 64-bit dividend with a 32-bit divisor producing |
| 18 | * a 64-bit result and a 32-bit remainder. To accomplish this optimally |
| 19 | * we call a special __do_div64 helper with completely non standard |
| 20 | * calling convention for arguments and results (beware). |
| 21 | */ |
| 22 | |
| 23 | #ifdef __ARMEB__ |
| 24 | #define __xh "r0" |
| 25 | #define __xl "r1" |
| 26 | #else |
| 27 | #define __xl "r0" |
| 28 | #define __xh "r1" |
| 29 | #endif |
| 30 | |
| 31 | #define __do_div_asm(n, base) \ |
| 32 | ({ \ |
| 33 | register unsigned int __base asm("r4") = base; \ |
| 34 | register unsigned long long __n asm("r0") = n; \ |
| 35 | register unsigned long long __res asm("r2"); \ |
| 36 | register unsigned int __rem asm(__xh); \ |
| 37 | asm( __asmeq("%0", __xh) \ |
| 38 | __asmeq("%1", "r2") \ |
| 39 | __asmeq("%2", "r0") \ |
| 40 | __asmeq("%3", "r4") \ |
| 41 | "bl __do_div64" \ |
| 42 | : "=r" (__rem), "=r" (__res) \ |
| 43 | : "r" (__n), "r" (__base) \ |
| 44 | : "ip", "lr", "cc"); \ |
| 45 | n = __res; \ |
| 46 | __rem; \ |
| 47 | }) |
| 48 | |
| 49 | #if __GNUC__ < 4 || !defined(CONFIG_AEABI) |
| 50 | |
| 51 | /* |
| 52 | * gcc versions earlier than 4.0 are simply too problematic for the |
| 53 | * optimized implementation below. First there is gcc PR 15089 that |
| 54 | * tend to trig on more complex constructs, spurious .global __udivsi3 |
| 55 | * are inserted even if none of those symbols are referenced in the |
| 56 | * generated code, and those gcc versions are not able to do constant |
| 57 | * propagation on long long values anyway. |
| 58 | */ |
| 59 | #define do_div(n, base) __do_div_asm(n, base) |
| 60 | |
| 61 | #elif __GNUC__ >= 4 |
| 62 | |
| 63 | #include <asm/bug.h> |
| 64 | |
| 65 | /* |
| 66 | * If the divisor happens to be constant, we determine the appropriate |
| 67 | * inverse at compile time to turn the division into a few inline |
| 68 | * multiplications instead which is much faster. And yet only if compiling |
| 69 | * for ARMv4 or higher (we need umull/umlal) and if the gcc version is |
| 70 | * sufficiently recent to perform proper long long constant propagation. |
| 71 | * (It is unfortunate that gcc doesn't perform all this internally.) |
| 72 | */ |
| 73 | #define do_div(n, base) \ |
| 74 | ({ \ |
| 75 | unsigned int __r, __b = (base); \ |
| 76 | if (!__builtin_constant_p(__b) || __b == 0 || \ |
| 77 | (__LINUX_ARM_ARCH__ < 4 && (__b & (__b - 1)) != 0)) { \ |
| 78 | /* non-constant divisor (or zero): slow path */ \ |
| 79 | __r = __do_div_asm(n, __b); \ |
| 80 | } else if ((__b & (__b - 1)) == 0) { \ |
| 81 | /* Trivial: __b is constant and a power of 2 */ \ |
| 82 | /* gcc does the right thing with this code. */ \ |
| 83 | __r = n; \ |
| 84 | __r &= (__b - 1); \ |
| 85 | n /= __b; \ |
| 86 | } else { \ |
| 87 | /* Multiply by inverse of __b: n/b = n*(p/b)/p */ \ |
| 88 | /* We rely on the fact that most of this code gets */ \ |
| 89 | /* optimized away at compile time due to constant */ \ |
| 90 | /* propagation and only a couple inline assembly */ \ |
| 91 | /* instructions should remain. Better avoid any */ \ |
| 92 | /* code construct that might prevent that. */ \ |
| 93 | unsigned long long __res, __x, __t, __m, __n = n; \ |
| 94 | unsigned int __c, __p, __z = 0; \ |
| 95 | /* preserve low part of n for reminder computation */ \ |
| 96 | __r = __n; \ |
| 97 | /* determine number of bits to represent __b */ \ |
| 98 | __p = 1 << __div64_fls(__b); \ |
| 99 | /* compute __m = ((__p << 64) + __b - 1) / __b */ \ |
| 100 | __m = (~0ULL / __b) * __p; \ |
| 101 | __m += (((~0ULL % __b + 1) * __p) + __b - 1) / __b; \ |
| 102 | /* compute __res = __m*(~0ULL/__b*__b-1)/(__p << 64) */ \ |
| 103 | __x = ~0ULL / __b * __b - 1; \ |
| 104 | __res = (__m & 0xffffffff) * (__x & 0xffffffff); \ |
| 105 | __res >>= 32; \ |
| 106 | __res += (__m & 0xffffffff) * (__x >> 32); \ |
| 107 | __t = __res; \ |
| 108 | __res += (__x & 0xffffffff) * (__m >> 32); \ |
| 109 | __t = (__res < __t) ? (1ULL << 32) : 0; \ |
| 110 | __res = (__res >> 32) + __t; \ |
| 111 | __res += (__m >> 32) * (__x >> 32); \ |
| 112 | __res /= __p; \ |
| 113 | /* Now sanitize and optimize what we've got. */ \ |
| 114 | if (~0ULL % (__b / (__b & -__b)) == 0) { \ |
| 115 | /* those cases can be simplified with: */ \ |
| 116 | __n /= (__b & -__b); \ |
| 117 | __m = ~0ULL / (__b / (__b & -__b)); \ |
| 118 | __p = 1; \ |
| 119 | __c = 1; \ |
| 120 | } else if (__res != __x / __b) { \ |
| 121 | /* We can't get away without a correction */ \ |
| 122 | /* to compensate for bit truncation errors. */ \ |
| 123 | /* To avoid it we'd need an additional bit */ \ |
| 124 | /* to represent __m which would overflow it. */ \ |
| 125 | /* Instead we do m=p/b and n/b=(n*m+m)/p. */ \ |
| 126 | __c = 1; \ |
| 127 | /* Compute __m = (__p << 64) / __b */ \ |
| 128 | __m = (~0ULL / __b) * __p; \ |
| 129 | __m += ((~0ULL % __b + 1) * __p) / __b; \ |
| 130 | } else { \ |
| 131 | /* Reduce __m/__p, and try to clear bit 31 */ \ |
| 132 | /* of __m when possible otherwise that'll */ \ |
| 133 | /* need extra overflow handling later. */ \ |
| 134 | unsigned int __bits = -(__m & -__m); \ |
| 135 | __bits |= __m >> 32; \ |
| 136 | __bits = (~__bits) << 1; \ |
| 137 | /* If __bits == 0 then setting bit 31 is */ \ |
| 138 | /* unavoidable. Simply apply the maximum */ \ |
| 139 | /* possible reduction in that case. */ \ |
| 140 | /* Otherwise the MSB of __bits indicates the */ \ |
| 141 | /* best reduction we should apply. */ \ |
| 142 | if (!__bits) { \ |
| 143 | __p /= (__m & -__m); \ |
| 144 | __m /= (__m & -__m); \ |
| 145 | } else { \ |
| 146 | __p >>= __div64_fls(__bits); \ |
| 147 | __m >>= __div64_fls(__bits); \ |
| 148 | } \ |
| 149 | /* No correction needed. */ \ |
| 150 | __c = 0; \ |
| 151 | } \ |
| 152 | /* Now we have a combination of 2 conditions: */ \ |
| 153 | /* 1) whether or not we need a correction (__c), and */ \ |
| 154 | /* 2) whether or not there might be an overflow in */ \ |
| 155 | /* the cross product (__m & ((1<<63) | (1<<31))) */ \ |
| 156 | /* Select the best insn combination to perform the */ \ |
| 157 | /* actual __m * __n / (__p << 64) operation. */ \ |
| 158 | if (!__c) { \ |
| 159 | asm ( "umull %Q0, %R0, %Q1, %Q2\n\t" \ |
| 160 | "mov %Q0, #0" \ |
| 161 | : "=&r" (__res) \ |
| 162 | : "r" (__m), "r" (__n) \ |
| 163 | : "cc" ); \ |
| 164 | } else if (!(__m & ((1ULL << 63) | (1ULL << 31)))) { \ |
| 165 | __res = __m; \ |
| 166 | asm ( "umlal %Q0, %R0, %Q1, %Q2\n\t" \ |
| 167 | "mov %Q0, #0" \ |
| 168 | : "+&r" (__res) \ |
| 169 | : "r" (__m), "r" (__n) \ |
| 170 | : "cc" ); \ |
| 171 | } else { \ |
| 172 | asm ( "umull %Q0, %R0, %Q1, %Q2\n\t" \ |
| 173 | "cmn %Q0, %Q1\n\t" \ |
| 174 | "adcs %R0, %R0, %R1\n\t" \ |
| 175 | "adc %Q0, %3, #0" \ |
| 176 | : "=&r" (__res) \ |
| 177 | : "r" (__m), "r" (__n), "r" (__z) \ |
| 178 | : "cc" ); \ |
| 179 | } \ |
| 180 | if (!(__m & ((1ULL << 63) | (1ULL << 31)))) { \ |
| 181 | asm ( "umlal %R0, %Q0, %R1, %Q2\n\t" \ |
| 182 | "umlal %R0, %Q0, %Q1, %R2\n\t" \ |
| 183 | "mov %R0, #0\n\t" \ |
| 184 | "umlal %Q0, %R0, %R1, %R2" \ |
| 185 | : "+&r" (__res) \ |
| 186 | : "r" (__m), "r" (__n) \ |
| 187 | : "cc" ); \ |
| 188 | } else { \ |
| 189 | asm ( "umlal %R0, %Q0, %R2, %Q3\n\t" \ |
| 190 | "umlal %R0, %1, %Q2, %R3\n\t" \ |
| 191 | "mov %R0, #0\n\t" \ |
| 192 | "adds %Q0, %1, %Q0\n\t" \ |
| 193 | "adc %R0, %R0, #0\n\t" \ |
| 194 | "umlal %Q0, %R0, %R2, %R3" \ |
| 195 | : "+&r" (__res), "+&r" (__z) \ |
| 196 | : "r" (__m), "r" (__n) \ |
| 197 | : "cc" ); \ |
| 198 | } \ |
| 199 | __res /= __p; \ |
| 200 | /* The reminder can be computed with 32-bit regs */ \ |
| 201 | /* only, and gcc is good at that. */ \ |
| 202 | { \ |
| 203 | unsigned int __res0 = __res; \ |
| 204 | unsigned int __b0 = __b; \ |
| 205 | __r -= __res0 * __b0; \ |
| 206 | } \ |
| 207 | /* BUG_ON(__r >= __b || __res * __b + __r != n); */ \ |
| 208 | n = __res; \ |
| 209 | } \ |
| 210 | __r; \ |
| 211 | }) |
| 212 | |
| 213 | /* our own fls implementation to make sure constant propagation is fine */ |
| 214 | #define __div64_fls(bits) \ |
| 215 | ({ \ |
| 216 | unsigned int __left = (bits), __nr = 0; \ |
| 217 | if (__left & 0xffff0000) __nr += 16, __left >>= 16; \ |
| 218 | if (__left & 0x0000ff00) __nr += 8, __left >>= 8; \ |
| 219 | if (__left & 0x000000f0) __nr += 4, __left >>= 4; \ |
| 220 | if (__left & 0x0000000c) __nr += 2, __left >>= 2; \ |
| 221 | if (__left & 0x00000002) __nr += 1; \ |
| 222 | __nr; \ |
| 223 | }) |
| 224 | |
| 225 | #endif |
| 226 | |
| 227 | #endif |