Decimal.fma

typeof(this) fma(
          const  typeof(
          this)  rhs,  const  typeof(
          this)  addend,
          ref  DecimalContext ctx)

const @safe pure nothrow @nogc

IEEE fused multiply-add: this * rhs + addend computed exactly and rounded once under the context. The ideal exponent of an exact result is the finer of the product's and the addend's.