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Status: Reported (1)

RFC 9426, "BATched Sparse (BATS) Coding Scheme for Multi-hop Data Transport", July 2023

Errata ID: 8477
Status: Reported
Type: Technical
Publication Format(s) : TEXT, HTML
Reported By: Marco Munizaga
Date Reported: 2025-06-23

Section 3.2 says:

   function DegreeSampler(j, DD)
       Let CDF be an array
       CDF[0] = 0
       for i = 1, ..., MAX_DEG do
           CDF[i] = CDF[i - 1] + DD[i]
       Rand_Init(j)
       r = Rand() % CDF[MAX_DEG]
       for d = 1, ..., MAX_DEG do
           if r >= CDF[d] do
               return min(d, K)
       return min(MAX_DEG, K)

                     Figure 7: Degree Sampler Function

It should say:

   function DegreeSampler(j, DD)
       Let CDF be an array
       CDF[0] = 0
       for i = 1, ..., MAX_DEG do
           CDF[i] = CDF[i - 1] + DD[i]
       Rand_Init(j)
       r = Rand() % CDF[MAX_DEG]
       for d = 1, ..., MAX_DEG do
           if r < CDF[d] do
               return min(d, K)
       return min(MAX_DEG, K)

                     Figure 7: Degree Sampler Function

Notes:

- if r >= CDF[d] do
+ if r < CDF[d] do

When sampling a degree from the degree distribution using the CDF, you should check that the random number is *less than* the CDF at that degree. As an example, assume the CDF is [0, 10, 100], and r is from [0,100). This means that d=1 should be chosen 10% of the time. The old code would choose d=1 90% of the time. It would also never choose any other value besides d=1, as later CDF values are guaranteed larger. If r was smaller than CDF[1] it is guaranteed to be smaller than CDF[2]

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