srli

srli moves bits right by a fixed amount and puts 0s in the vacated top positions. It is the constant-amount form of srl, which covers the mechanics and the zero fill. The i means immediate, a constant encoded in the instruction.

The form of srli appears below, where amount is a fixed number from 0 to 31.

srli rd, rs1, amount

A right shift halves a number once for every place moved, and the zero fill treats the value as never negative, so srli divides an unsigned number by a power of two with no remainder. The next line divides t0 by four.

srli t0, t0, 2

Combined with a masking AND, srli extracts one field from a packed value. Shift the field down to the bottom, then apply andi to keep only its bits. Reading the second byte of a word takes a right shift by 8 and an AND with 0xff.

The RISC-V manual encodes constant shifts as a specialization of the I-type format, one of the standard instruction layouts. The shift amount occupies the lower 5 bits of the immediate field, and bit 30 of the instruction distinguishes the two right shifts. srli performs a logical right shift, and 0s enter the upper bits.

srli always fills with 0s. That suits raw bit patterns and numbers that are never negative. On a signed value that may be negative, the 0s overwrite the sign marker. Signed division by a power of two uses srai. The choice between the two reflects how you read the bits of the register.