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After compilation math.di interface is generated with errors. Return type for "clamp" and "smoothstep" functions is missing (must be "auto"). It can be not related to specific compiler version, but it used to work properly with previous compiler version.
This looks like a dmd bug to me, related to the .di generation.
use CommonType instead of auto, to address #28
This should be fixed now, please reopen if it sill occurs.