diff options
Diffstat (limited to 'include/asm-arm/div64.h')
| -rw-r--r-- | include/asm-arm/div64.h | 180 |
1 files changed, 179 insertions, 1 deletions
diff --git a/include/asm-arm/div64.h b/include/asm-arm/div64.h index 3682616804ca..37e0a96e8789 100644 --- a/include/asm-arm/div64.h +++ b/include/asm-arm/div64.h @@ -27,7 +27,7 @@ #define __xh "r1" #endif -#define do_div(n,base) \ +#define __do_div_asm(n, base) \ ({ \ register unsigned int __base asm("r4") = base; \ register unsigned long long __n asm("r0") = n; \ @@ -45,4 +45,182 @@ __rem; \ }) +#if __GNUC__ < 4 + +/* + * gcc versions earlier than 4.0 are simply too problematic for the + * optimized implementation below. First there is gcc PR 15089 that + * tend to trig on more complex constructs, spurious .global __udivsi3 + * are inserted even if none of those symbols are referenced in the + * generated code, and those gcc versions are not able to do constant + * propagation on long long values anyway. + */ +#define do_div(n, base) __do_div_asm(n, base) + +#elif __GNUC__ >= 4 + +#include <asm/bug.h> + +/* + * If the divisor happens to be constant, we determine the appropriate + * inverse at compile time to turn the division into a few inline + * multiplications instead which is much faster. And yet only if compiling + * for ARMv4 or higher (we need umull/umlal) and if the gcc version is + * sufficiently recent to perform proper long long constant propagation. + * (It is unfortunate that gcc doesn't perform all this internally.) + */ +#define do_div(n, base) \ +({ \ + unsigned int __r, __b = (base); \ + if (!__builtin_constant_p(__b) || __b == 0 || \ + (__LINUX_ARM_ARCH__ < 4 && (__b & (__b - 1)) != 0)) { \ + /* non-constant divisor (or zero): slow path */ \ + __r = __do_div_asm(n, __b); \ + } else if ((__b & (__b - 1)) == 0) { \ + /* Trivial: __b is constant and a power of 2 */ \ + /* gcc does the right thing with this code. */ \ + __r = n; \ + __r &= (__b - 1); \ + n /= __b; \ + } else { \ + /* Multiply by inverse of __b: n/b = n*(p/b)/p */ \ + /* We rely on the fact that most of this code gets */ \ + /* optimized away at compile time due to constant */ \ + /* propagation and only a couple inline assembly */ \ + /* instructions should remain. Better avoid any */ \ + /* code construct that might prevent that. */ \ + unsigned long long __res, __x, __t, __m, __n = n; \ + unsigned int __c, __p, __z = 0; \ + /* preserve low part of n for reminder computation */ \ + __r = __n; \ + /* determine number of bits to represent __b */ \ + __p = 1 << __div64_fls(__b); \ + /* compute __m = ((__p << 64) + __b - 1) / __b */ \ + __m = (~0ULL / __b) * __p; \ + __m += (((~0ULL % __b + 1) * __p) + __b - 1) / __b; \ + /* compute __res = __m*(~0ULL/__b*__b-1)/(__p << 64) */ \ + __x = ~0ULL / __b * __b - 1; \ + __res = (__m & 0xffffffff) * (__x & 0xffffffff); \ + __res >>= 32; \ + __res += (__m & 0xffffffff) * (__x >> 32); \ + __t = __res; \ + __res += (__x & 0xffffffff) * (__m >> 32); \ + __t = (__res < __t) ? (1ULL << 32) : 0; \ + __res = (__res >> 32) + __t; \ + __res += (__m >> 32) * (__x >> 32); \ + __res /= __p; \ + /* Now sanitize and optimize what we've got. */ \ + if (~0ULL % (__b / (__b & -__b)) == 0) { \ + /* those cases can be simplified with: */ \ + __n /= (__b & -__b); \ + __m = ~0ULL / (__b / (__b & -__b)); \ + __p = 1; \ + __c = 1; \ + } else if (__res != __x / __b) { \ + /* We can't get away without a correction */ \ + /* to compensate for bit truncation errors. */ \ + /* To avoid it we'd need an additional bit */ \ + /* to represent __m which would overflow it. */ \ + /* Instead we do m=p/b and n/b=(n*m+m)/p. */ \ + __c = 1; \ + /* Compute __m = (__p << 64) / __b */ \ + __m = (~0ULL / __b) * __p; \ + __m += ((~0ULL % __b + 1) * __p) / __b; \ + } else { \ + /* Reduce __m/__p, and try to clear bit 31 */ \ + /* of __m when possible otherwise that'll */ \ + /* need extra overflow handling later. */ \ + unsigned int __bits = -(__m & -__m); \ + __bits |= __m >> 32; \ + __bits = (~__bits) << 1; \ + /* If __bits == 0 then setting bit 31 is */ \ + /* unavoidable. Simply apply the maximum */ \ + /* possible reduction in that case. */ \ + /* Otherwise the MSB of __bits indicates the */ \ + /* best reduction we should apply. */ \ + if (!__bits) { \ + __p /= (__m & -__m); \ + __m /= (__m & -__m); \ + } else { \ + __p >>= __div64_fls(__bits); \ + __m >>= __div64_fls(__bits); \ + } \ + /* No correction needed. */ \ + __c = 0; \ + } \ + /* Now we have a combination of 2 conditions: */ \ + /* 1) whether or not we need a correction (__c), and */ \ + /* 2) whether or not there might be an overflow in */ \ + /* the cross product (__m & ((1<<63) | (1<<31))) */ \ + /* Select the best insn combination to perform the */ \ + /* actual __m * __n / (__p << 64) operation. */ \ + if (!__c) { \ + asm ( "umull %Q0, %R0, %1, %Q2\n\t" \ + "mov %Q0, #0" \ + : "=&r" (__res) \ + : "r" (__m), "r" (__n) \ + : "cc" ); \ + } else if (!(__m & ((1ULL << 63) | (1ULL << 31)))) { \ + __res = __m; \ + asm ( "umlal %Q0, %R0, %Q1, %Q2\n\t" \ + "mov %Q0, #0" \ + : "+r" (__res) \ + : "r" (__m), "r" (__n) \ + : "cc" ); \ + } else { \ + asm ( "umull %Q0, %R0, %Q1, %Q2\n\t" \ + "cmn %Q0, %Q1\n\t" \ + "adcs %R0, %R0, %R1\n\t" \ + "adc %Q0, %3, #0" \ + : "=&r" (__res) \ + : "r" (__m), "r" (__n), "r" (__z) \ + : "cc" ); \ + } \ + if (!(__m & ((1ULL << 63) | (1ULL << 31)))) { \ + asm ( "umlal %R0, %Q0, %R1, %Q2\n\t" \ + "umlal %R0, %Q0, %Q1, %R2\n\t" \ + "mov %R0, #0\n\t" \ + "umlal %Q0, %R0, %R1, %R2" \ + : "+r" (__res) \ + : "r" (__m), "r" (__n) \ + : "cc" ); \ + } else { \ + asm ( "umlal %R0, %Q0, %R2, %Q3\n\t" \ + "umlal %R0, %1, %Q2, %R3\n\t" \ + "mov %R0, #0\n\t" \ + "adds %Q0, %1, %Q0\n\t" \ + "adc %R0, %R0, #0\n\t" \ + "umlal %Q0, %R0, %R2, %R3" \ + : "+r" (__res), "+r" (__z) \ + : "r" (__m), "r" (__n) \ + : "cc" ); \ + } \ + __res /= __p; \ + /* The reminder can be computed with 32-bit regs */ \ + /* only, and gcc is good at that. */ \ + { \ + unsigned int __res0 = __res; \ + unsigned int __b0 = __b; \ + __r -= __res0 * __b0; \ + } \ + /* BUG_ON(__r >= __b || __res * __b + __r != n); */ \ + n = __res; \ + } \ + __r; \ +}) + +/* our own fls implementation to make sure constant propagation is fine */ +#define __div64_fls(bits) \ +({ \ + unsigned int __left = (bits), __nr = 0; \ + if (__left & 0xffff0000) __nr += 16, __left >>= 16; \ + if (__left & 0x0000ff00) __nr += 8, __left >>= 8; \ + if (__left & 0x000000f0) __nr += 4, __left >>= 4; \ + if (__left & 0x0000000c) __nr += 2, __left >>= 2; \ + if (__left & 0x00000002) __nr += 1; \ + __nr; \ +}) + +#endif + #endif |
