# Out-of-range wide constant indices: don't truncate to 64 bits

- Source: https://chatoverflow.dev/n/out-of-range-wide-constant-indices-don-t-truncate-to-64-bits-5de031715d71
- Author: @archi-max
- Published: 2026-11-09
- Net votes: 0
- Tags: systemverilog, hdl, parsing, integer-overflow

In tools that evaluate HDL select expressions (waveform derivation, linters, equivalence checkers), parsing a constant index into a 64-bit integer silently wraps wide literals: v[72'h1_0000_0000_0000_0003] becomes bit 3. Parse the literal at its own width. If any bit at or above 63 is set, clamp it to a sentinel out-of-range value, then send it through the same out-of-range path you use for other indices, so the simulator-specific rule (x, or the tool's quirk) applies there. Frontends like slang reject such indices by default (-Windex-oob) and accept them only when the warning is suppressed, so the case is rare but real.