diff options
Diffstat (limited to 'net/dccp/ccids/lib/tfrc_equation.c')
| -rw-r--r-- | net/dccp/ccids/lib/tfrc_equation.c | 28 |
1 files changed, 13 insertions, 15 deletions
diff --git a/net/dccp/ccids/lib/tfrc_equation.c b/net/dccp/ccids/lib/tfrc_equation.c index ddac2c511e2..90009fd77e1 100644 --- a/net/dccp/ccids/lib/tfrc_equation.c +++ b/net/dccp/ccids/lib/tfrc_equation.c @@ -13,7 +13,6 @@ */ #include <linux/module.h> -#include <asm/div64.h> #include "../../dccp.h" #include "tfrc.h" @@ -616,15 +615,12 @@ static inline u32 tfrc_binsearch(u32 fval, u8 small) * @R: RTT scaled by 1000000 (i.e., microseconds) * @p: loss ratio estimate scaled by 1000000 * Returns X_calc in bytes per second (not scaled). - * - * Note: DO NOT alter this code unless you run test cases against it, - * as the code has been optimized to stop underflow/overflow. */ u32 tfrc_calc_x(u16 s, u32 R, u32 p) { - int index; + u16 index; u32 f; - u64 tmp1, tmp2; + u64 result; /* check against invalid parameters and divide-by-zero */ BUG_ON(p > 1000000); /* p must not exceed 100% */ @@ -650,15 +646,17 @@ u32 tfrc_calc_x(u16 s, u32 R, u32 p) f = tfrc_calc_x_lookup[index][0]; } - /* The following computes X = s/(R*f(p)) in bytes per second. Since f(p) - * and R are both scaled by 1000000, we need to multiply by 1000000^2. - * ==> DO NOT alter this unless you test against overflow on 32 bit */ - tmp1 = ((u64)s * 100000000); - tmp2 = ((u64)R * (u64)f); - do_div(tmp2, 10000); - do_div(tmp1, tmp2); - - return (u32)tmp1; + /* + * Compute X = s/(R*f(p)) in bytes per second. + * Since f(p) and R are both scaled by 1000000, we need to multiply by + * 1000000^2. To avoid overflow, the result is computed in two stages. + * This works under almost all reasonable operational conditions, for a + * wide range of parameters. Yet, should some strange combination of + * parameters result in overflow, the use of scaled_div32 will catch + * this and return UINT_MAX - which is a logically adequate consequence. + */ + result = scaled_div(s, R); + return scaled_div32(result, f); } EXPORT_SYMBOL_GPL(tfrc_calc_x); |